Building a gaming pc for portability purposes. What case should I get?

I've decided to build another gaming PC for being able to haul it between houses. My brother and I like to play games when I come over to his house and I usually bring my regular pc that plays games well but it's a little to big and annoying to keep hauling back and fourth. I was looking at some cases on amazon but don't know which one would be best to fit a good sized gpu in.

Any cases that you would recommend that can fit inside a backpack easily?