This schematic is for a tower that allows the Truncoctagon to be placed on relatively flat terrain.
As the Truncoctagon has been so popular, some of you might find this add-on useful.
The tower itself is 23 blocks square plus an extra two on one side for the access stairs. When the base is placed at sea-level the tip of the structure sits at the height limit. (This includes the original Truncoctagon on the top.)
The tower itself is simply an extension of the support column used in the original structure and contains sufficient repeating sections which can be removed so the structure can be placed on higher terrain if desired.
The overall structure has been slightly modified to allow a beacon beam to be fired up its axis. There are two coloured glass blocks that modify the beam colour, both are up the top in the original structure, a red one on the ceiling of one of the lower rooms and a blue one in the quadrapod structure right up on top, these should be removed if you desire a white beam emerging at the top.