Building a small doghouse/playhouse in Brooklyn front yard?

The guys in my family are building a little “doghouse”/playhouse out of lumber. It’s a great project but now the youngest wants to put it in our tiny front yard. It would be flush with our front fence and visible from the sidewalk. The footprint would be about 4 ft x 4 ft. I just checked zoning regs for R5B buildings and the closest I could come to anything like this is a regulation about “sheds” in *back*yards. Anyone have experience with this sort of little outbuilding? I think it’s a bad idea and could be an eyesore. Wondering if it’s also against NYC building code. Anyone know? Thanks !