While I know using 24"x24" table 'tiles' increases the number of joints (and therefore helps in guessing ranges/distances), I still think they have merit due to their flexibility. The discussion over at Strictly Average inspired me to post some of my past terrain thoughts (which are now on hold, due to the Waaaagh!)
The idea: Instead of flat 24x24 modules, build simple 5-sided boxes so that the main playing surface is elevated. This gives you the freedom to go both above 'grade' and below.
Also, while I like the idea of modular hills, I don't think I'll include them in the table tiles. Done separately from the table, the hills would be more flexible and could hide the table joints/measuring aides.
See part 2 of this modular table idea here.
See how to make the buildings here.