[Shop-talk] Building/adding a deck cover?

[Obaa]

Hi all,
I'm in the planning process of adding a deck cover to our rear deck; the goal is to have a sheltered area that I can move the kids' stuff to from the garage, and free up space there (Actually got this idea from a previous thread from someone doing something similar).  The deck is a second-story deck (our lot has a steep slope), and is roughly 9' deep x 30' wide.  It faces west, and thus gets a beating from the sun in the afternoons, with ambient temps in the 90's (to possibly low 100's on occasion) during the summer.  For most of the rest of the year, it is wet and drizzly (Portland, OR).  No snow load to speak of, but there is the possibility of high winds (60+mph) a few times a year.
I wanted to do something quick and temporary, since we were thinking of razing the deck in the next 2-3 yrs and adding an addition, but with the way things are, this cover might be in service for significantly longer.  According to the county, no permit is required for anything under 200 sq. ft. and freestanding, so this is what I'll stick to.
I went shopping at Lowe's over the weekend, to see what I could find.  I found some Tuftex corrogated panels (www.tuftexpanel.com/polycarb.htm), which I thought would make a reasonable roof.  They have two grades, one with lifetime warranty, and the other with 0 warranty; a call to Tuftex support indicated that they expected replacement between 2-10 years, so I think I'm sticking with the higher grade stuff.
Regarding framing the cover, it needs to be standalone, so I can't attach it to a ledger board.  I think I can form a sufficient stable base if I use brackets to attach 4x4 pillars to the deck directly above where the current supports are.  To attach the roof, I found a local lumber liquidator that has a large number of half-gable trusses with an acceptable pitch (1 in 3) which I can shorten to the correct length.  The trusses are triangulated pretty well, but are only made of 2x2's (they were originally made for manufactured homes).  How can I calculate if these are strong enough?  (the panels are ~15lbs each, supported on 14" centers).
What would be really nice would be finding some free design software like HD has for building decks, but for designing covers or roofs.  Sadly, my google-fu skills are not good enough.  Does anyone know of any they can send my way?

Thanks!