It's a very small build, which is absolutely fine. It's going to seriously constrain your block choices and limit any potential technical builds, which is sometimes fun trying to overcome.
My advice would be to try to do something that you wouldn't think is possible in a space that size. For example, and only if you want a real technical challenge, you could try your hand at a shulker-based storage system with all of the redstone and actual storage hidden underground, with the above-ground footprint just an input and output where your filled/empty shulker boxes go.
But if something like that sounds too complicated, my overall suggestion still stands: just try to do something that seems impossible in that space at first blush. It doesn't have to be technical. Decorating small spaces like that is enough of a challenge!