Trusses are built to order, based on your local codes, loads, use, and dimensions. Here in northern VA, I can get by with ag-use for a pole barn, which allows four foot spacing on trusses. Naturally, they need to be sized for that. I got 36" trusses from Home Depot earlier this year, delivered to my site, for a little over $100 each. That includes the engineering paperwork package that an inspector will need to see.