Building a fpga rig is very straightforward. This is what you do:

1. Buy one or more of the fpga products, ie, BFL bitforce, Icarus, or modminer quad. If the company doesn't sell them anymore you will need to buy from another person.
2. Plug them into your computer's USB port. Buy a hub if you run out of ports.
3. Join a mining pool and run the mining software.

You now own an fpga rig.