My basement playroom is 11 x 30 and then a smaller 8x10 area off to the side where we have our books, stuffies, and my teaching stuff.

Upstairs we use the diningroom which is 11 x 13 and truthfully the five of them play in there just fine. The trick is what is available and when. Your space will allow you to have some of the larger things out too which for me are basement only items.

Don't put too much on the walls or at least all of the walls or the room will start to close in. Designate one long wall for displays which will emphasize the length of the room. Across one of the short ends put shelves on the entire wall and out of rotation toys, resources can be stored on the shelves. That allows the parents to see everything available to the kids even if they aren't out. If you make the bottom shelf 24" you can use this at child height as a play table and it is great for the fisherprice playsets either for play or storage. We have the long shelf along the entire length of the room and 12" shelves above for storage. Keep as much of the floor space open and the room will feel bigger and give you more play options.

It isn't size of space that appeals to parents as much as what is available in that space.