Hey KEA, Where I work doing steel erection, we always have roof joist left over. The kind like they use in the homedepot's. There great for what your looking for. If you look at my mill building you can see that I used 20 footers and welded 5' angle iron to the ends to make them 30 feet long. You could look around there and when you see one of these buildings going up, go talk to the steel erector and ask if you could have any left over joist. ONLY talk to the steel forman. The job supper WILL say no. You tell the steel forman you will give him $20.00 ea. I'll be willing bet you'll have your joist pretty fast.