I had my handyman build one of these in front of our house. Also, I make a hobby of biking around to circulate books between different little free libraries in my extended neighborhood. I've found some amazing books over the years, things that were very different from my typical prior experience of books. I like this aspect, that it can be eye opening. Each little free library has it's own style of books. Some are better at handling magazines. Some see a lot of book movement, some much less. These factors influence how I move books around from one to another.

Suggestions on building a little free library: 1) By far the number one priority: Waterproof. If it's not waterproof, in my opinion you're actually doing a disservice to the community, rather than a service. And have an angled roof for proper drainage. 2) Don't make it too deep. Definitely not more than 18 inches. Probably 15 inches is a good depth. 3) If you can, make two levels: One level for tall books, another level for short books. 4) Don't make it too tiny, because then it's hard to get books in and out of. 5) A good solid stand so it doesn't fall over. 6) A good latch that will resist wind. Magnetic is good. I also like to have a magnet plus a hook that can be used for backup. Also with time it's nice to have the second option in case the shape changes a little and the magnet doesn't work. 7) You might try making a mockup out of cardboard so you can see the physical size and get a sense of how many books will fit. 8) Not a building tip, but: Try to arrange the books to look nice. If you have few books you can face some of them to attract attention.