I know few build from scratch today. For those that do Kent has a great building board on sale.

They call it a shelf. It is edge to edge laminated softwood. Being made of 5 or 6 pieces glued together tends to keep it straight.

It is also very thick at 1-3/8ths inches thick. It is 12x48" and only $20 at the Kent in Bayers Lake. Located over near the special order desk in Lumber and Building Materials dept. About 35 mm thick for the metric contingent. 305x1220mm overall.

Fastening a piece of 1/2" or 3/8th gyproc on top makes it easy to insert pins and cheap to replace the top when you have too many holes in it. I used to use stair treads but this is thicker and bigger.