How did you construct the displays that sit on the shelves and other flat surfaces?

All of my displays are built on wall insulating foam cut from 3/4" x 13 5/8 x 48" sheets. First I cut a piece of foam that will cover the entire shelf or other surface it will sit on. This becomes the base piece that everything else is mounted on. I put it in place on the shelf, then arrange the houses that will be in the display on top of it, moving them around until I get the look I want. If some of the houses need to be elevated, I add additional layers of foam cut a little larger than the base of the house they will support until I get the height I want. Once I get all the houses in place and elevated as desired, I trace around the base of each house or, if it sits on another piece of foam to elevate it, around the bottom piece of foam in the stack. I then write the name of each house on the piece of foam it sits directly on so I don't forget where each piece goes. with that done, I remove all the houses and glue all the foam in place with a hot melt glue gun set on low heat to prevent the glue from melting the foam.

Once I have everything glued in place, I put the foam back on the shelf and put all the houses in place again to check the look one more time. If I make any changes at this point, I repeat this step until I'm happy with the arrangement.

Next, I remove all the houses one more time, add any backdrop behind the display I have decided on, and put the wiring in place that will light the houses. I try to chain the wire and lights such that one wall plug will power the entire display. I plug them into X-10 remote on/off controllers (which I purchased at Radio Shack) so I can turn multiple displays on with the push of a button instead of having to run all over the house plugging things in. (CAUTION: Make sure no wires are pinched or circuits overloaded during this stage of assembly. If your house burns down the displays won't look very good!) With all the wiring safely assembled and in place I cover the entire display with Buffalo Snow (see its description in a subsequent question), pulling the lights through the snow so they can be put in the houses when they are put back in place.

The houses are then put back on the display, inserting the lights as I go, and any accessories I want to add are put in place. The final outcome looks like this.