How do I design a shed to make optimal use of building materials?

Part of the trick is in looking at what sort of lengths you'll need, and then figure out how to optimize the cuts. Odds are, there will be some sort of shorter pieces needed (eg, header, sill and cripple studs around the windows), and so you can sometimes get less waste by mixing multiple parts on a board. If you don't have parts that need under-23" boards (cribbing for the floor?), look to see if you have something that's needs ~47", and get 12' sticks rather than 10'. Now, if you make things too complicated, then you'll be wasting more time figuring out the right cuts than just building, and if someone's building to sell, man-hours are cost, so they've got to balance things out. If you're doing it yourself, you might consider your time to be free, and you'd make a different decision on if the reduced scrap is worth it. (this sort of thing almost seems like something for a computer program ... put in all of the lengths & quantities, and it makes recommendations on what sticks to buy and how to cut it ... it'd be easier than planning on cuts on sheet goods) Another consideration is the exact opposite of BMitch's ReStore recommendation (which is a great idea ... also check to see if there are architectural salvage places if you're adding onto an existing older building to keep the doors, trim & radiators similar) ... but find someone to give the scrap to. My step-father one year made a bunch of angels as christmas decorations made primarily out of the end scraps of 2x4s. He rips it down as corner reinforcement for birdhouses, etc. Odds are, there's going to be someone else who can use what you consider to be scrap, but it's a matter of finding the right person. .. and I'd personally never make a 200 sq.ft. shed ... because at 150sq.ft is when you have to get a permit in my county, and that requires plans (structural, site, etc.) ... which means I have no flexibility if on the day when I got to buy lumber I get some length other than my original plan called for, and I decide to change things around at the last minute. (so yes, sheds are different from larger buildings, in that regard) also odds are, there's someone else with the same obsession for lack of waste that has some plans out there that have the roof pitch / eve length set to minimize waste.

This is pretty reminiscent of a very common calculus problem, and the most important thing, which hasn't been mentioned yet, would be to build it square or nearly square. 10'x10' = 100 sq ft 15'x5' = 75 sq ft Both have 40' perimeters, but the square version has 33% more interior area. 8'x12' is perfectly fine (96 sq ft), but don't get too carried away with a rectangular shape. Outside of that, just worry about the pieces that are over 5' and numerous: the studs (primarily) and the rafters... perhaps a few others, depending on the roof design. Keep in mind that the rafters/joists lengths can be calculated quite easily. With a 30/60/90 triangle, the sides are 2, sqrt(3), and 1 (times some coefficient, forming triangles such as 4 x 3.464 x 2, which would cover a span of 8', plus or minus a foot, depending on how you make them.) Another triangle that you could use is 36.87/53.13/90, which produces a triangle with sides that are multiples of 3, 4, and 5. A lot of this stuff is going to be affected heavily by the type of rafter design that you want, e.g. rafter tails, collar ties or joists spanning the top plates, etc.