Construction Cost Planner
Estimate projects, generate quotes, manage budgets with line-item precision
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A price you can defend rests on two independent numbers: a top-down figure per square foot, and a bottom-up total built from quantities you counted. Within a few percent of each other, sign it. Thirty percent apart and one of them is wrong. You want to know which before the concrete truck is booked.
One example runs through every step: a 30 ft × 40 ft detached workshop. 1,200 sq ft on a slab, 4:12 gable roof in exposed-fastener metal, a 16 ft × 30 ft storage mezzanine, drywalled interior, a 12 ft × 90 ft gravel drive, 200 lin ft of fence.
Step 1: Set the anchor with the Construction Cost Estimator
Start top-down. Two minutes of work, and it is the only independent check you will have on the take-off later. Enter 1,200 sq ft, pick build type and quality, set contingency to 10%.
1,200 sq ft × ~$155/sq ft = $186,000 anchorDo not quote this figure. Its only job is catching an order-of-magnitude error back in Step 5.
Step 2: Take off each trade on its own geometry
Roof area
The footprint is 1,200 sq ft. The roof is not. A 4:12 pitch multiplies plan area by about 1.054, giving roughly 1,265 sq ft of roof plane. Hand that to the Roofing Calculator with Waste Factor as a plain gable with no valleys and it comes back with about 1,392 sq ft to order, or 14 squares.
Fasteners
Screws are a count, not an area, and they are the item most often remembered once the crew is already on the roof. The Metal Roofing Screw Calculator works from panel width, purlin spacing and eave length: about 1,120 for 14 squares. Buy 1,250. Some get dropped and some get over-driven.
Mezzanine deck: run the span check first
The Mezzanine Floor Calculator gives 480 sq ft of deck and the design load for the use you pick. Take that load to the Joist Span Calculator before you price anything, because the span answer rewrites the bill of materials. Here, 2×10s at 16 in on centre will not clear 16 ft at storage load. So you either go heavier and tighter, or drop a beam and two posts at mid-span and make each run 8 ft. The beam wins: 24 joists instead of 40.
Interior board
Perimeter walls (140 lin ft × 10 ft), partitions and the 1,200 sq ft ceiling come to about 3,800 sq ft of board. The Drywall Mud and Tape Calculator turns that into roughly 1,450 lin ft of tape and 17 gallons of compound (four buckets) against 86 sheets of 4×12.
Site work
The drive is 12 ft × 90 ft at 4 in compacted depth: 13.3 cubic yards net. The Gravel Calculator for Driveway adds for compaction and converts to weight, landing near 21 tons. For the fence, 200 ft at 8 ft centres is 26 posts. The Concrete Calculator for Fence Posts takes hole diameter and depth, deducts the post itself, and returns about 30 cubic feet, or 50 eighty-pound bags. Buy 55.
| Trade | Net take-off | Ordered | Example material $ |
|---|---|---|---|
| Gravel drive | 13.3 cu yd | 21 tons delivered | 680 |
| Metal roof | 1,265 sq ft | 1,392 sq ft (14 sq) | 4,320 |
| Roof fasteners | 1,120 screws | 1,250 | 190 |
| Mezzanine | 480 sq ft | 24 joists + beam, posts, deck | 3,650 |
| Drywall | 3,800 sq ft | 86 sheets, 17 gal mud, 1,500 ft tape | 1,670 |
| Fence post concrete | 30 cu ft | 55 × 80 lb bags | 340 |
| Slab, framing, siding, doors, MEP rough | : | supplier quotes | 64,150 |
| Materials total | 75,000 |
Step 3: Waste is a property of the layout, not a safety margin
The most expensive habit in estimating is ordering to net area. Net area is what ends up on the building, and it is never the quantity you buy. The gap between the two comes out of geometry rather than carelessness.
Panels cover 3 ft. The eave is 40 ft. That is 13.33 panels, so you buy 14: 42 ft of coverage for 40 ft of roof, and no amount of care on site recovers the difference. Add a valley and it gets worse, because both planes cut on an angle and the offcuts are handed, so what comes off the left plane will not fit the right. A cut-up roof wastes more than a plain gable. That is why the calculator asks about hips, valleys and dormers instead of applying one flat percentage: the number should move with the layout rather than sit at a habitual 10%.
Every trade works the same way. Drywall: 3,800 sq ft over a 48 sq ft sheet is 79.2 sheets, and nobody hangs 0.2 of a sheet. Deductions are worse. Estimators take window and door openings off the net area, but you cut those openings out of full sheets, so the deduction saves nothing and under-orders the job. Gravel: 4 in is compacted depth, and loose stone settles. Post concrete: holes belly out at the bottom, and you cannot return half a bag.
Step 4: Contingency is a different pot of money
Waste is a known physical loss with a known cause. Compute it and it lives inside the quantity. Contingency is money held against events you cannot list in advance: rock in the footing trench, rot behind siding you have not opened, a price move between quote and order.
Blur the two and you make one of two errors. Use waste as the contingency and the extra sheets get used, as they always do, so the first surprise eats into margin. Double count instead, running 10% waste on every quantity and then a 10% materials contingency on top of already-wasted quantities, and you price yourself out of a bid you should have won.
Contingency also shrinks as unknowns resolve. As a rule of thumb, a new build on a clean pad with a full drawing set carries less than a renovation where you open up existing structure. Set it once, in one field. Never per trade.
Step 5: Roll it into the Job Costing Calculator
The bottom-up total: $75,000 materials from the table, 940 labor hours at $48, $18,500 of subcontract for the slab pour and electrical rough.
75,000 materials + 45,120 labor + 18,500 sub = 138,620 direct
+ 12% overhead = 155,254 cost
÷ (1 − 0.18) target margin = 189,334 priceHad the take-off come in at $240,000 against a $186,000 anchor, do not split the difference. Find the line. It will be a trade priced at retail that should be subcontracted, an hour count with nothing behind it, or a quantity in the wrong unit.
The 940 hours is the weakest input here. Log actuals with the Time Card Calculator and compare at each trade handover rather than at the end. If framing burns 130 against 100, the interior is still ahead of you to adjust.
Step 6: Confirm margin, not markup
An 18% margin and an 18% markup are different prices. Quote one while budgeting the other and the job finishes profitable on paper and short in the bank. Markup of 18% on $155,254 gives $183,200. Margin of 18% gives $189,334. The $6,134 between them is roughly a week of crew wages.
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Permits and inspections sit outside every number above
Every step above prices materials, labor and margin, and both methods agree within 2 percent by the time you reach the anchor check. Neither one touches permits, and that omission can move both the cost and the timeline more than any single line item in the take-off table.
A detached workshop like the example almost always needs a building permit, and depending on the jurisdiction, separate electrical and plumbing permits if the build includes either. Permit fees vary widely by county, commonly a percentage of declared project value or a flat schedule by square footage, and they're worth pricing as a real line item rather than a rounding error folded into contingency. The bigger cost is usually time, not money: inspection scheduling can add one to three weeks per required inspection stage, foundation, framing, rough electrical, final, depending on how backed up the local office is, and a crew standing idle waiting on a sign-off costs real labor dollars even though nothing on the estimate sheet shows it.
Call the local building department before finalizing the bid, not after, and build a realistic inspection-wait figure into the schedule the same way waste gets built into the material take-off.