Did anyone mention that the pad or disk sander should be a random orbital type?
I don't see how anyone can really build without a table saw. I guess it can be done, but not by me. I know, it was already mentioned...just adding my $.02. And a power miter (i.e. cut-off or chop) saw is a time saver. I have table, miter and band saws.
Meriam's idea of the baggie must be using it like an icing bag? That is, to squeeze it out of a corner that's been cut out? Neat idea.
Besides clamps, 15'-20' long ratchet type cargo straps are handy for bending down the ply to the roof curve.
Since you have a frame, you won't need heavy duty metal working equipment.
Screwdrivers...cordless, powered of course with magnetic bit holders and lots of bits. I have a Dewalt cordless drill, but bought two of the HF 18V cordless drills, one in a kit with other attachments (some of which I have even used). Even if you only use one at a time, you have the extra battery. I often kept a drill bit in one, and screwdriver bit in the other. Having this tool is handy too.
It allows you to use one drill to drill countersunk holes, then reverse the bit to put in the screw. Several companies make a version of this one.