I ordered a tower last Friday, from here:
It arrived Tuesday, and I was soon unwrapping it and assembling it. Basic but well worth the price. It is a bit unsteady until both cross bars have been fitted, then with the outriggers fitted, and levelled up, it was very stable. There were 2 slightly tight sections, but otherwise it slotted together without a fault. I bought 5 5' scaffold boards from a local supplier - £18, and screwed in sections of 3x2 wood on the bottom to stop them moving about when placed on the platform. I didnt need the extra 2'6" section to get good access to the guttering, but with that fitted, it gives a better protection against falling over the edge!
If you are in the market for one, I dont think you can get better for occasional use. Alan.