Free Realms is interested to see what your answer might be, because they've removed the biggest impediment to building whatever you want: that big, inconvenient house in the middle. Well, to be fair, houses aren't inconvenient when you want one there, but they do sort of get in the way of a giant hedge maze, or obstacle course, or tribute to yourself in real estate form.
There are two types of lot currently available, a Briarwood lot and a Snowhill lot. Each one can hold a grand total of 1,500 items, which gives players more than enough freedom to build almost anything. The one catch is that the lots do cost Station Cash, but that's the nature of the free-to-play beast. Free Realms has always had an interesting mix of elements, both sandbox-oriented and quest-oriented, and this one skews toward the side of a sandbox -- which is what you can literally build, if you so desire.