The wood for Bitbeam is easily sourced at any major art supply store. (Ask for the craft/hobby woods section.) Basswood is recommended over balsa, as basswood is stronger. Next, head to your nearest laser cutter and start cutting your bitbeams.
Bitbeam height and width is 5/16 inches. Each hole is 4.8 mm in diamater and 8mm apart from each other -- just like Lego Technic.
The advantage of building your own Bitbeam parts over Lego is that 1) the materials are cheaper, 2) I can make parts in sizes that Lego doesn't make, and 3) playing with lasers is fun!