The same design in all four steps: 72" walls, a 6/12 roof, 8 mm twin-wall polycarbonate, 2 benches and 20 psf of snow.
01 Drawn
Every stud, rafter and sheet placed
Boards
81
Sheets bought
11
Vents
5 roof, 6 side
02 Checked
10 applicable rated checks passed
10 applicable rated checks passed for this configuration. Site-specific requirements are not fully assessed. 16 checks run in all; the rated ones compare the design with an extension guide, a maker's table or our stated default.
Structure: frame and glazing6/6
Roof slope for the glazing
Roof supports for the snow load
Wall supports for wind
Rafter span
Sheet lengths
Door fits the end wall
Vent openings, by area2/2
Roof vents
Side vents
Layout: benches and size2/2
Aisle
Bench depth
What a pass does not mean. The checks size the structure and the vent openings. They do not predict the temperature or humidity inside: that depends on your climate, shade, heating and how you run the vents.
Left to you and your building department: snow load, building permit, tie-down, size, sheet orientation and sealing, screw spacing.
03 Priced
About $3,813.80 in materials
Lumber$791.49
Glazing$1,264.98
Profiles and sealing$779.20
Fasteners and hardware$326.93
Vents and door$549.42
Base and site$101.78
32 of 34 lines at dated shelf prices, before tax and freight. Gravel is estimated separately at $56 to $186. Hiring the build out: $2,300 to $6,600, kept apart.
Stores, dates and what the total leaves out
Read at Home Depot, Hamilton Mill store, PolycarbonateStore.com, Greenhouse Megastore, Lowe's, Atlanta-Edgewood store, Home Depot, Bronx Terminal store, Sturdi-Built Greenhouse, Amazon.com, shipped, Sep 30, 2026 to Oct 13, 2026.
Not included: gravel (estimated separately at $56 to $186); tax; shipping or freight. Twin-wall sheets usually ship by freight, which can add a lot: get a delivered quote.
04 Built in order
6 phases, 46 to 66 hours
Our estimate for one handy person with a helper. Each picture is this design at the end of its phase, the new parts in color.
01Gravel bed and base
Check: diagonals equal within 1/4 in, base level.
02Wall frames
Check: corners plumb both ways, top plates level.
03Roof frame
Check: rafter tops in one plane: a string along them touches each one.
04Door and benches
Check: door swings clear, benches level.
05Twin-wall glazing
Check: every hole pre-drilled, washers snug, not crushed.
Materials, pricedSame frame and vents; only the glazing, its profiles and its supports change.
$3,813.80
$2,852.73
Roof supports at 20 psfFrom each maker's published load table, end spans reduced.
24" apart at most
24" apart at most
Highest snow in the maker's tableAbove it the planner does not size the roof.
about 31 psf
50 psf
Lowest roof slopeThe makers' minimum fall.
2/12
1.5/12
Sheet widthCorrugated panels lap one corrugation.
48"
26", 23" covered
Light, clear sheetMaker's figure; no comparable number for SUNTUF in our sources.
80% (Palram, 8 mm)
no figure in what we read
Heat loss, 40 F in, 10 F outModeling assumptions, not tested performance: the twin-wall U is Palram's published figure; no U for SUNTUF is published in what we read, so the corrugated line uses UGA's single-layer panel figure as a stand-in.
7,701 Btu/h
14,459 Btu/h
Free and paid
Design it free. Build it from the $29 plan.
Free, no account
Your design in 3D, every change redrawn
Every planner check, with its rule and source
The materials list, priced line by line
A summary PDF of the design
$29 once, for your design
Every wall framed, each stud and girt dimensioned from the corner
Every polycarbonate sheet numbered, with its cut and the stock sheet it comes from
The cut list, every cut assigned to a store board
Vents or the exhaust fan, the door and the benches, each on its own sheet
The shopping list with store prices and the build, phase by phase
One PDF for the greenhouse you designed, on Letter paper: 36 sheets for the 8x12 gable greenhouse. Every wall framed and dimensioned, the roof framing, every polycarbonate sheet numbered and cut face by face with its profiles, tapes and screw spacing, the cut list and the board plan, vents, door and benches, the shopping list with prices, and the build in order with a check at each phase.
Yes. Designing, the checks, the materials list with prices and the summary PDF are free, with no sign-up. You pay only if you want the builder's plan for your design.
Twin-wall sheets have air channels that hold heat better and spread the light; they need sealing tapes and end profiles. Corrugated panels cost less and the maker tables them to higher snow loads: about $2,853 in materials for our 8x12 corrugated plan. The designer prices both for your size.
The roof snow load your building department uses for your town. The designer spaces the roof supports from the glazing maker's published table for that load. The 8 mm twin-wall sheet on our 8x12 is tabled to about 31 psf; above the table the designer does not size the roof and says so.
It depends on your town. The model code exempts small accessory buildings up to 200 sq ft, but many towns use a smaller number, and setbacks, height limits and HOA rules can apply either way. Ask your building department before you buy materials; the planner shows your floor area against that number but does not check local rules.
If you find an error in your plan, we fix it or refund you. Within 30 days of buying, email us your order number, the sheet and what is wrong. If we cannot fix it, we refund you in full. The details are in our terms.
Illustration
Illustration
Your greenhouse, your numbers
Grow longer, in a greenhouse that fits your yard.
Change the size, the roof, the glazing, the vents and the benches. The roof supports, the vents and the materials list follow every change. Free, no account.
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