Pegasus is a good scale for 28mm 30mm heroic. Off hand I can't say the height of the floors, but I can measure at home if you'd like. I believe they are in the 2.5 - 3 inch range. They're at least 2.5 inches, and I think they are 3 inches. The scale is basically the same as GW terrain kits.
In terms of quality, I have been very pleased with Pegasus products. The casting is good quality, the pieces go together tightly, and they are strong. It is the type of terrain that will stand up to a good deal of abuse. They aren't the most lovingly detailed terrain sets you can get, but the detail is nice the way it is, and the pieces paint up well.
If you get a set, be careful about dry fitting. I always like to dry fit pieces before applying glue, but as I mentioned, the Pegasus kits fit together very tightly. If you dry fit the pieces completely flush, it can sometimes be difficult to separate them again. I suppose that this could be a benefit depending on what you are trying to do.
The Gothic cathedral kits also come with three variant bits for the walls: lanterns, torches, and blank plugs to make a bare wall. These bits are very useful when working on additional terrain projects and add nice value to the kits.