The essence of a great cat playroom is kitting out the room with lots of of toys and climbing structures that keep the cat entertained.
Consider using modular items that expand the play area for a cat.
Even with a small space available you can create a fun area for cats to enjoy using. Just consider what items your going to have, things like a scratching post, a interactive toy or a place to sit down in will often be enough.
If your fortunate to be able to allocate a large space to a cat then consider creating different play zones with different toys and furniture in each zone.
