Shed Designer can pick the roof overhang for you. Until today it chose the longest overhang that needed no more lumber money than the shortest. On the default 8x12 that rule picked 9", because the rafters and sub-fascia cost the same from 6" to 9".
The rule priced only the boards, though. An eave also adds roof sheathing, shingles, drip edge and trim. So the tool now builds the design at every whole inch from 6" to 18", prices each whole order at the starting prices, and takes the longest within an allowance of the cheapest. The allowance defaults to $25 and has its own field beside the tick box.
Here is what each overhang costs on the default shed (lumber, then the whole order before tax):
| Overhang | Lumber | Whole order |
|---|---|---|
| 6" to 8" | $738 | $3,103 |
| 9" | $738 | $3,143 |
| 10" | $742 | $3,146 |
| 11" to 12" | $742 | $3,167 |
| 13" to 14" | $742 | $3,206 |
| 18" | $742 | $3,242 |
Lumber barely moves across the whole range: $4 from end to end. The steps are in the roofing. At 9" the roof needs a fifth bundle of shingles ($40.47), and the old rule bought it without noticing, because shingles weren't part of its sum.
The tool now picks 8", which costs no more than 6", and says why in the design notes: "overhang 8", the longest from 6" to 18" at the lowest materials cost, and 9" would add $40.47." An allowance of $50 gives 10" (+$43.82), and $70 gives 12" (+$64.50). The search adds about 4 ms to each rebuild of the design.
Because the cost of an overhang is lumpy, a dollar allowance buys as much eave as the money allows, which a fixed number of inches can't. Set $0 for the cheapest, or a larger amount if your walls need more protection from the rain.
These are screening estimates from listed prices, and the tool's automatic choice uses the starting prices, not the ones you type. It is not engineering, and a long overhang in a windy area needs its own check. Try Shed Designer.