Not bad at all - a few thoughts....
Plywood is kinda pricy, while you can do a lot better if you get most everything from a sawmill. Rough-sawn boards and framing are plenty good enough for a shed and might well look better, board and batten style. The exception to that is the floor framing and floor, I'd use pressure treated wood for the deck framing and 3/4 ply for the floor itself. Also, the 2x6 floor joists are a little light, it'd be bouncy and might well sag if there's weight on there for any length of time.
Rather than the truss roof, a roof with 2x6 rafters will work okay. And if it's all open, the ridge vent ( a PITA ) isn't necessary. Especially if you have a window or two on the gable ends.
A couple of cross members are good for overhead storage, though I might just make half of it a loft. That's where trusses are no fun, they can really screw up your overhead storage.
9x13 - ahmmm- I might go 10 x 12. Less waste if you use plywood.
This set of plans specifies asphalt shingles. But what's called 'rolled roofing' is cheaper and goes on kinda idiot-proof if you follow the directions.
Used windows and such are a beautiful thing. Often free, along with a lot of other used materials, for the shed-builder on a budget. And frequently better made than the vinyl-clad cr@p they sell nowadays. Gives it a little character too.
Use galvanized nails. Trust me on this one. Bright ( uncoated) nails rust, and stainless nails ...look, you wanna build a 20 year shed with 100 year nails, knock yourself out, but you're wasting your money.
Something like this can be built with a circular saw, measuring tape, a 16 oz hammer, a framing square, a chalkline, a utility knife and a level, and I've built more than a few with no more than that. Oh, a ladder and a shovel too. More tools are nice, but no need to go nuts.
hope that's of use
doc...