I usually challenge myself to build weird houses. I had a vampire that had a completely underground home that was designed for entertainment.... That one was an odd build to make. Instead of windows, I put the wall fish tanks in a couple of spots where they looked interesting.
I'd show pictures, but that was on my last computer.
I challenged myself (inspired by the challenge on this site) to build the smallest house I could. Didn't get anywhere near as small as some, but it was fun. Then I challenged myself to do the biggest house I could. Ten bedrooms, dedicated rooms for each skill, a walled courtyard in the middle, Shang Simla architecture. It was a thing of beauty.... And, it crashed my old computer when I went back to live mode! LOL
At one point, I built a "house" that had a bunch of tiny apartments in it and used the whole roommates thing from University to collect rent from them all. (Ah, door permissions are a wonderful thing.) That was... amusing. Didn't have a job, just collected rent periodically. I skilled that Sim up a lot and wound up bored beyond belief. Took a while to get to the bored part, though, since I had some fun influencing the various roommates to do things.... Maid service is a must, by the way, or you run around harassing everyone to clean.
You also wind up as pretty much a slum lord, since living off of those rent checks takes maxing the number of roommates, building tiny apartments and using lousy furnishings. Communal kitchen, etc.
Theme houses can be amusing, too. Build a Oriental theme on this lot. Egypt over here. That one is going to be French. This one is a castle, and there's a converted asylum. This house here might be a private museum.... etc.