Here's a teaser of two of the towers I designed:
Click on it for a bigger image.
The tower on the left is Tier 1. The right-side tower is Tier 4. So, you can see how they evolve as they're upgraded.
EDIT: Here's an in-game shot of me testing the methods and design:
The left tower is already upgraded to T2. The right one is still T1.
Everything seems to be working as well as I expected. I am on my personal server and using the /give command for all of the materials. I'm probably going to build a stretch of it the real way. Mine materials with stone or iron tools and then see how long it will take to build. Shouldn't be too long. I've collected materials for MUCH bigger projects fairly quickly, so I'm optimistic.