Drew these floor plans for a 24 x 36 foot two story garage with gambrel roof. Priced it out at local lumber yards in May 2008 and the wood, siding, roofing, nails, anchor bolts, basically everything but the cement, wiring, and doors was $2995. Cement I figured would be about $1200. Plot work is not figured in and could be done by hand for those who like to work hard. Our local code requires a turn down foundations, but you might consider a Calfornia Slab, or if they'd look at it, a gravel floor with a cement sidewall foundation.
With the beam, the trusses are over engineered to be constructed on site. The beam allows for heavier storage in the upper level. However most contractors prefer the ease of having trusses manufactured and delivered, which estimated out at another $1200. Without the beam, the engineered joists of the trusses can span the garage but they'll support less weight. If you do want to build your trusses on site, the honest old fashioned way, you're probably going to have a hard sell down at the county building code office. You'll need to make it easy for them to show that it meets/exceeds engineering specs, otherwise they'll want to nick you for a couple of grand to hire a certified engineer. Isn't it great we have an international building code now?
Please feel free to download and use the plans if you can use them. I'll keep looking for the material list, but if you make one send it so I can post it here. Thanks.