large indoor cat house suggestions?

Good morning! One on my students has an emotuonal support animal (a cat) but her school has asked her to keep it in a confined when she is not there. The student is on a tight budget. Does anyone have either: -a blueprint of how to build one large enough so the kitty can have a litter box, etc. - suggestions of where to find one large enough that does not cost a couple hundred dollars. Thanks in advance!! Gina