28qt tubs should be fine for most BPs, unless you have a large female which require 41qt tubs. There is a debate on when or if to move them into 41qt tubs, but you'll be just fine with a 28qt rack system.

So far I've built one out of melamine, and one out of plywood, but if I were to build another one it will be out of expanded PVC (XPVC).
Here is a thread on how to build one out of XPVC.

XPVC will be lighter than melamine, and both will be more durable over time and easier to clean than plywood.

I haven't looked too much into pre-made racks, but the ones mentioned above should all be high quality.