GPU Hardware Requirement Help

Hello ,
friends.

Can you help me in deciding to make an home made local brute force machine that can crack that the password hashes of length upto 20 length
and having uppercase , lowercase , digits and some special chars.

I found these machines like:

1. An brute force machine : YouTube

2. 25 -GPU Brute Force : Securit Ledeger

Can any body tell me that how can i build it in home if i will buy the hardware from outside.
How i will be able to connect my GPU's in parallel in motherboard to work them together.

I am confused will anybody help me.

Thanks,
Pacific