I have looked far and wide to find the best tower defense development resources. Here are a few of the tutorials I’ve found floating around the internet.

World Editor Tutorials
This extremely comprehensive guide covers pathing, spawning units, tower abilities, leaderboards, boss levels, upgrades, breakpoints, balancing and much more. In addition to the tower defense builder walkthroughs this site also covers all manor of other WC3 maps.

Fischk
From the developer of Massacre TD. This site doesn’t have as much info on TD map making but you can find a lot of useful WC3 downloads.

Antistone’s Warcraft 3 Maps
This is a site documenting and offering downloads of several Antistone maps. He also includes a page about ideas for TD development.

Epic War
This site doesn’t offer much info on building WC3 maps. I’ve included Epic War because it’s a great place to upload and promote your maps for others to play.

WC3 Map Development Forum
This is probably one of the best places to go if you want to learn from the pros.