This is a picture book from the early 80s. My mom thinks it came from a mail order book club. Kids in an apartment building have amphibian pets: turtles, alligator. . . the alligator gets stuck in a tree. Balloons get him out (or got him in?). At the end the kids get a rooftop garden for their pets. Over the course of the story you see an ornate fountain being built in town.
The Alphapets’ ‘Albert the Absent-Minded Alligator’?
It sounds like a Stephen Kellogg book.
It’s neither of the titles mentioned above but I am so grateful to you for putting on your thinking caps! The illustrations had a lot of white on the page, not as dense as Stephen Kellogg, if that makes sense.