As Bryan mentioned, you always want to plan your pieces so that you can bend parts perpendicular to the grain, whenever possible. This and other important building information can be found in places like AC-43.13 and books like "Kit Airplane Construction" by Ron Wanttaja
(which I highly recommend reading. Its on Amazon.com here:
http://www.amazon.com/Kit-Airplane-Cons ... n+wanttaja )
Another alternative is to go attend an EAA SportAir workshop. Their basic class on Sheetmetal aircraft is super-valuable, and they hold the classes all over the US throughout the year.
As for metal sources, I found
http://www.onlinemetals.com to be a good supplier for sheets, angles, and channel-stock.
Good luck in your build!
--Noel
P.S. Be careful buying pieces from eBay and other secondary sources. You can get great deals sometimes; but you need to make sure the factory printing on the metal is still visible, identifying it as 6061-T6 (and check it thoroughly for any signs of corrosion, of course)