I went the cheap route with 1" PVC. I drilled holes in the bottom PVC, and about 1' up from the bottom on the uprights.
1 inch is fine. I used to build massive 10 feet by 10 feet cages so that's why I got stuck on the 1 1/2 inch PVC. I've since downsized and canibalized the PVC from the larger cages.
I just learned something new. I build a cage that was much deeper than it was square. When I pulled it up to the shore to put fish in, it worked great to tip back with most of it under water.