How much would you like to spend? I know a few who did that for their kids, one got PVC goal posts and painted floor and walls without finishing the surfaces, and another one did pretty much the same thing only he painted a goal on the block wall and screened the window.

If you want to spend extra you can do fake grass outdoor carpet or a glue-down flooring and finish walls with something durable so you don't need to fix or paint every time a ball hits it.

Good luck