How to Assemble a Garden Shed (Stratco / Absco)
I put up my first Stratco shed when I was about twenty, helping my old man build a workshop on his property in Mandurah. He’d dug the slab himself, levelled it with a builder’s level he’d had since the 70s, and made me check the diagonals with a tape four times before he’d let me touch a single panel. Twenty years later that shed is still dead-square and bone-dry. The thing nobody tells you when you buy a shed kit is that the slab matters more than the shed. A $1,200 Absco Eco on a bad slab will warp, leak, and rust out at the base inside five years. The same kit on a properly prepped base will last 20-plus years and still look new at year 10. Worth doing once, worth doing right.
Good news is you don’t need a concreter. There’s a quick-pour DIY slab for under $400, and there’s a “no concrete at all” option using compacted road base with a treated-pine perimeter that costs under $150 and works just as well for a 3x3m shed in a typical suburban backyard. I’ll cover both.
What you’ll need
- Your Stratco or Absco shed kit, with the instruction booklet
- A second adult — non-negotiable for the wall and roof stages
- Either: 60 x 20kg bags of N20 concrete + reinforcing mesh + form timber (slab option); or 1 cubic metre of road base + 4 lengths of 100×100 H4 treated pine + 16 GalvBugle screws (compacted-base option)
- A cordless drill with Phillips and Tek-screw bits — Makita, Ryobi, Ozito all fine
- Tin snips for ridge cap trims
- A 1.2m spirit level and a measuring tape
- Builder’s twine and four star pickets
- A rubber mallet
- Plate compactor from Kennards ($80/day) for the compacted-base option
- Selleys Roof and Gutter silicone, neutral cure
- Dynabolts M10 x 75mm to anchor the frame to slab or timber base
- If you’re in cyclone or high-wind territory (north QLD, coastal NSW, Top End): proper cyclone tie-down anchors
Step 1: Check your council planning rules first
Five minutes on the council website saves a $2,000 demolition order later. Search “[council name] outbuildings exempt development”. Key thresholds usually:
- Footprint 10 or 20 square metres depending on council
- Boundary setback 900mm (some councils 1,500mm)
- Maximum height 2.4m eaves or 3.0m ridge
- Not in front of the building line
- Bushfire BAL-rated zones have extra cladding rules
The catch that bites every second DIY shed builder: the 10 square metre threshold is the eaves footprint, not the floor area inside. A 3.0 x 3.4m shed with 200mm eaves comes to 11.56 square metres and needs a permit. Read the wording carefully.
Step 2: Mark out the shed footprint with string lines
Use star pickets and builder’s twine to mark the four corners of the shed base. Add 100mm extra each side beyond the shed footprint — that’s your slab or compacted-base perimeter. Check the diagonals are equal: the 3-4-5 triangle method, or just measure both diagonals end-to-end. If they’re equal, the rectangle is square. Re-check the 900mm setback from boundaries with the tape. Point the doors toward an open direction not a fence — strong winds plus an open shed door equals a bent door track. Out here in Perth the Fremantle Doctor will catch any door you leave swinging into the breeze.
Step 3a: SLAB option — quick-pour your own concrete
Skip this if youre going compacted-base. Excavate 100mm deep across the slab footprint. Form up with H3 treated pine 100×50 set on edge. Lay SL62 reinforcing mesh on bar chairs 50mm above the ground. Hire a concrete mixer from Kennards ($60/day) and mix 60 x 20kg bags of N20. Pour, screed flat, float, broom-finish for grip. Cover with plastic and water-cure seven days before standing the shed.
Step 3b: COMPACTED-BASE option — road base + treated-pine perimeter
Excavate 100mm deep. Lay 4 lengths of 100×100 H4 treated pine around the perimeter, screwed at each corner with 150mm GalvBugle screws — that’s your edge restraint. Check level with the spirit level and shim under the timber as needed. Fill the inside with road base (CBR 80 from a quarry, or Bunnings bulk bags). Compact in two layers of 50mm with a hired plate compactor — wet the road base lightly between layers, not soggy. Finished surface should be hard enough that a boot heel barely dents it. This base is dimensionally stable, drains well, and accepts the shed-frame Dynabolts directly into the timber edge. If youre also planning a paver path up to the shed door, check our lay-pavers guide while youre carting road base.
Step 4: Build the floor frame on the base
Most modern Absco and Stratco kits include a steel floor channel that bolts into a closed rectangle. Lay it on your slab or base. Square it up by measuring the diagonals — must be equal within 5mm. Mark Dynabolt positions through the floor channel holes onto the slab, or the timber edge for compacted-base. Drill 10mm holes, 70mm deep, with a hammer drill. Don’t drill all eight holes before installing — drill one, install one, move to the next. If the channel shifts you’ll mis-align everything and end up redrilling.
Step 5: Assemble the wall panels — flat first, then stand
Wall panels go together flat on the ground. Most Absco wall panels are pre-assembled — you slot the corner posts in and screw them together. Stratco wall panels are flat-pack: sheet, frame channel, then sheet over. Build all four walls flat before standing any of them. Two people can stand and join one wall at a time. Trying to do it solo guarantees a bent panel — you’ll catch a corner on the slab, twist the sheet, and there’s no fixing a twisted sheet metal panel once it’s bent.
Step 6: Stand walls in opposing-pair order
Rear wall first, then front wall, then sides. Hold each in place with temporary bracing — a 90×35 pine offcut screwed to the wall and to the slab edge. Tek-screw the corner joins from the inside, snug only. Don’t fully tighten until all four walls are connected and squared. Final squaring happens after the roof goes on.
Step 7: Fit roof beams and sheeting
Roof structure varies by kit. Absco uses pre-formed gable trusses, Stratco uses Z-purlins. Fit them per kit instructions. Sheet the roof from one end to the other, lapping each sheet over the previous by one corrugation. Tek-screw at every second corrugation along each purlin. Run a bead of Selleys Roof and Gutter sealant along each lap before screwing — sounds excessive, but it’s the difference between a 5-year and a 20-year shed in WA’s heat-rain cycle. The Perth coastal salt air is brutal on any unsealed joint — out west the wind takes care of anything you’ve left half-finished.
Step 8: Fit ridge cap and barge boards
Ridge cap covers the apex. Tin-snip to length, sit it over the ridge with butyl tape underneath, screw at every corrugation. Barge boards (the gable-end trims) cover the cut sheet edges — same idea, butyl tape behind. Don’t skip the butyl tape. Aussie storms drive water uphill under the cap during high-wind events, and without sealing the shed leaks at the apex every time. If youre coastal, run an extra bead of Selleys behind the butyl for good measure.
Step 9: Hang the doors last
Sliding or swing doors are the last thing on. Track-mounted sliders need the track perfectly horizontal — check with the spirit level and shim if needed. Swing doors hang on heavy-duty galvanised hinges. The kit usually supplies butt hinges that are adequate but not flash. If you want better, swap to T-hinges from Bunnings ($25 a pair). Door alignment is make-or-break for the daily user experience: a door that drags or wont latch is the thing you’ll curse every weekend for the next 15 years. Take 20 minutes here. Get it right.
Step 10: Sealant pass and tidy-up
Walk around the inside with the silicone gun and seal every panel-to-panel join, every corner, the door track lower edge. From outside, seal the bottom edge of the wall panels to the slab or base — stops driving rain entering at the base. Sweep the slab clean. If you’re in north QLD or coastal NSW, this is the moment to fit your cyclone tie-down anchors per the kit’s wind-rating guidance. Don’t skip those — a shed lifting off a slab in a cyclone is a missile.
When to call a tradie or pro
If your shed footprint exceeds council exempt-development thresholds, you need a building permit and likely a registered builder. Same if you’re going larger than the kit’s wind rating (most consumer kits are N2 wind class, which doesn’t cover cyclonic regions). For cyclonic North QLD or Top End coastal sites, you need an N4 or C2-rated shed and an engineer’s tie-down spec — that’s not a Bunnings kit, that’s a Ranbuild or Fair Dinkum Sheds custom build. If you’re running power into the shed for lighting or a workshop, that’s licensed electrical work — no DIY. A sparky will come out, install the sub-board and circuits, and certify it.
Common screw-ups
- Bad slab or base: the shed wont save itself. A kit on a soft base lasts five years. Get the base right.
- Eaves-counted footprint over the threshold: the 10sqm rule includes eaves. Measure carefully before ordering.
- Skipping butyl tape under ridge and barge: guaranteed apex leak in the first big storm.
- Door track not level: drag, jam, broken roller — fix it before you finish, not later.
- No cyclone tie-downs in coastal zones: sheds lift in cyclones. Anchor properly.
Cost & time
A 3x3m Absco Eco kit is $700-900 from Bunnings. Slab cost adds $300-400. Compacted-base alternative adds $120-150. Plate compactor hire $80. Total for the DIY route, base and shed: $1,000-1,400. Time: one weekend for two people, including curing if you go compacted-base. Slab option adds a week of cure time before standing the walls.
Slab matters more than the shed itself. A great kit on a bad base lasts five years; an average kit on a great base lasts twenty. Compacted road base with a treated-pine perimeter is genuinely as good as a slab for a typical garden shed and saves you $400. Check that 10 square metre threshold against the eaves footprint not the floor, get the diagonals dead square, butyl tape under everything that overlaps, and you’ll be done. If your shed is going to live next to a paved area or a hedge run, see the paver path guide and the hedge trimming guide — both pair well with a weekend shed build. No dramas.
