Someone commented on the earlier Townscaper video I made about how to create floating propeller driven buildings and that they need more space to create one.
In this video I show how to use one of the small ovals on the grid and connect it to another to make a more complex floating structure. Finding the right place to build on the grid takes a little searching, but by slowly expanding it in a straight line vertically or horizontally seems to help. You can only expand it so far in one direction before having to start deleting bricks on the opposite side.
Hope that this helps!