I've tried a few different methods over the years, and the simplest has been the 2" foam board. Yes it's a little messy, but nothing a vacuum cleaner can't handle. Rough cuts with a kitchen knife, and smaller hills and valleys can be easily sanded onto the board. The only thing I haven't researched is the best method of adding multiple foam boards together to add elevation. Hot melt and contact cement are not the answer. Maybe white glue would work, and I'm sure there are others. I think someone mentioned something called super 78 high tack glue, but I haven't tried it yet.
Using this method you can always have a basically level surface at your disposal. All buildings (as long as they are built correctly) are built plumb and level. A tilted house just won't look right. As you work your way up the mountain you can plan your roads into each ascending level and then once completed add the road surface. For scenery, I used a qt of mis-mixed walmart latex white, and I added a little brown acrylic to it for a kinda dry earth color. I painted it on and sprinkled Woodland Scenics ground foam right on the wet paint. I followed this up with a 50/50 mix of water and white glue sprayed through an old windex bottle (very important to make sure the pump mists, you'll disturb the ground foam with it on stream!!)
If you want more coverage, sprinkle more foam on, then mist the glue mix again. You can sprinkle another light layer of foam on the wet glue, and vacuum the loose stuff off. This leaves a nice durable coating. The foam is solid enough to handle stuff. For trees, once it's all dried, poke an awl in the foam and stick the tree right into the hole. Cut the bases off pre-made ones for a more realistic effect.
One other advantage of using the blue (or pink) foam is you can work in sections. I used it for about 1/2 of my slot car/train table, and I was able to trace and cut out sections on newspaper, transfer the section onto the foam, and cut it outside, so there was no mess to clean up. Then after checking for fit, I started shaping and sculpting (also done outside).
In this example, I wanted a parking lot for my Pizza Hut... Pix tell the story..
For something like this, you paint in stages. Paint the parking lot (.99 acrylics from wally world craft dept). Let dry. Paint the curbing grey (same type paint) and let dry. Then paint the grassy areas brown, and sprinkle the foam on. It'll only stick to the wet stuff. Let dry. Glue water mix it ( use a piece of cardboard to keep the glue off the pavement) and a light sprinkle of foam and you're done.
Darn, I miss that table...
Yes, the scales are off, but I'm no rivet counter. I've always mixed die cast with HO trains since I was a kid (still am at 50).
