The garage I am designing will have an apartment above, so I am looking for info on this subject too.

Here's what I got back: About 30% more for trusses that allow some storage (20lb/sq ft), but really only between the trusses (i.e., parallel to truss) and about 100% more (i.e., double) for trusses that create a box and allow 40lb/sq ft.

Thanks heimert

If it's 100% more, you should price out conventional framing.

or consider this system. i think i'll be using it http://www.socketsys.com/

Here is a link that might be useful: lumber link

I just purchased 30' wide, gambrel attic storage trusses. Paid $104 per truss. They give me a 16' wide by 8' high attic. Spaced 16" on center I get 100+ psf floor load.

I know its not exactly what you are looking for, but it might help.