My most basic rule of thumb is to use a regular model and have a window come up to its waist. Total floor heights are 3". Thickness of floor becomes an irrelevant issue as long as the floors are 3" apart in total. Also, I don't trust the
GW plastic terrain, it's completely out of scale. The doors on the mechanicus pieces are titanic by comparison to the models that are supposedly using them. They're like twice the height of a space marine. That's 16 feet! As far as I know there is no "standard size" of anything for terrain, tournament or otherwise. Build stuff that you think looks cool, I say. Take a peak at my terrain
here for examples of what I mean.
Automatically Appended Next Post: Also, tiered hills I believe are about an inch or two per tier, but again, use your own aesthetic eye.