Shed Truss 12:12 Pitch

I can not tell you about the truss sizes for a whole bunch of reasons but I can tell you this -

Your joists need to be sized to the roof AND the weight that you plan to store up there. Normal trusses are not usually designed for the added load, just the roof.

This IS where and engineer is required. Here in Maryland, in my county, the plans would have to be done by a licensed engineer/architect before the permit is approved.

-- Love woodworking and fixing most anything

You don’t need an engineer, for simple things like this you can use prescriptive load tables. The American Wood Council span tables for joists and rafters will get you most of the way (they’ve also got a super handy span calculator), and some cities publish their own.

Second floors are usually designed for 40 lbs/sq.ft., so if you’ve got 18” on center spacing, use the span tables for 60 lbs and you’ll be good for a second floor. Roof loads depend on your climate; here in coastal Northern California we just get rain, if you’re in an area where snow will accumulate… (and if you’re in an area where snow will accumulate on that high a peak… well….).

I threw some #2 northern Doug Fir 2x6 into the AWC span calculator and got 9½’, so 2×6 will work awesomely on 16” centers, 2×4 will be light (might work for the actual rafter rather than the truss, but Arcata California's span tables don't have 2x4s useful for any horizontal application).

-- Dan Lyke, Petaluma California, http://www.flutterby.net/

I think you missed some sizes from your roof or you wrote incorrect info. I see that you are a great specialist in design, i need my essay written in 3 hours and I have to include some graphics there. Maybe you can help me?