As it implies, it looks like a wooden shed containing what looks like to be a type of woodchipper (a.k.a the Bloonchipper.)
You need at least 15, one tile with 3x3 space & 450 after completing the Bloonprint Hideout mission. It takes 30 minutes to construct & for each one built will yield a bloonchipper for use as seen in the top right-hand corner of the image provided.
Though this building increases the Bloonchipper population, It spawns an Engineer Monkey citizen. This is likely the the monkey who built the bloonchipper.