Illustrated Book on Tree Houses
This is a black and white illustrated book on tree houses of almost impossible designs, of a Rube Goldberg or Dr. Seuss complexity, full of multiple levels, ropes, block and tackles, ladders, wooden shingles, stove pipes, etc. I remember the illustrations looked like Erik Blegvad’s style of crosshatching, but it may not be him. Very fun book I got from the church library when I was ten, so it would date from the 1960’s.
It sounds like you might be looking for The Wonderful Treehouse by Harold Longman, illustrated by Harry Devlin (1962, published by Parents Magazine Press). The story is about a boy imagining all sorts of fanciful tree houses in the oak tree outside his window.
You could also be thinking of “Andrew Henry’s Meadow” written and illustrated by Doris Burn, 1965. Andrew Henry’s family is frustrated with him, because their house is filled with his Rube Goldberg inventions. He moves to a meadow and builds his own fancy tree house. Other kids arrive and he builds each of them a house that serves their particular interest, like fishing or dancing. Eventually, all of the families come to find their children and make compromises about how much space the kids can use at home for their hobbies.
That’s it! Found a nice copy, too. Thanks for helping me find this!