First, throw together 9 tank treads. For a bigger tower, more links.
Next, we use 3/4 pins to connect some Technic liftarms.
Clip it together. This is the basis for the round shape. It won't hold its shape yet, the tiles will force it to be circular at the end.
The next step is to bulk up the diameter with more liftarms. For bigger towers, the diameter would need to be bulked up a bit more. If the tiles don't fit, increaase the diameter. If there is a significant gap between tiles, decrease the diameter. Add a plate to increase the radius by the height of one plate. Add a liftarm to increase it by 2.5 plates worth.
Interleave them. There's nothing holding the two pieces together yet. Once the tiles get added, they'll stay together.
Throw some 1x10 plates together with a couple of 1x6 plates. This is what we're going to attach tiles to. It also bulks up the radius by another 2 plates, so height is important.
Make 17 more. (More for a larger diameter tower)
Now we've got everything we need, now start putting it together.