This years project for the kids at school is to model five scenes from "The Hobbit" in 28mm scale. Its quite an ambitious project if I do say so myself, as these are 10 and 11 year old kids. Follow my progress in the Works in Progress section if you're interested. The miniatures we'll be using are from Games Workshop Lord of the Rings wargame, and should stand in as the main characters very well I think.
I`m working on a series of models for a `Hobbit` project this winter for a Grade 5 class. It involves modelling Hobbiton and Dale in 28mm scale, so there`s quite a few buildings to make up. I started off using balsa for the wall sections, and was a bit frustrated, first at the cost, then and the challenges of cutting it, especially in circles.
I was walking through Michaels craft store getting some paint, when the idea struck me to use those thin sheets of foam that the use for a miriad of craft purposes. Its a fraction of the cost, and doesn`t have a grain to impede cutting like the balsa does. Any texturing you want can be done in after, and stabiity can be added
by either using interior braces from cheap popsicle sticks, or by mold casteing as I do.
So thats my brain storm for the day. Now I`m making good progress and spending way less.

My vote is for Weldbond white glue. I have a box of about a dozen various glues, and the one I go back to again and again is the weldbond. According to the maker...
Weldbond®  is a universal adhesive that bonds most anything! It is non-toxic, nonflammable, free of fumes, has low VOCs, is created without animal by-products and environmentally friendly!

For my purposes, weldbond dries quickly (but not too fast)to a clear, paintable finish.  Its super strong and water soluble.
Its good stuff, do yourself a favour and pick some up at your local hardware store.

As with most excellent ideas on terrain making, this isn`t mine. But I think its a great idea and I wanted to share it with others.
In nature, we see terrain that rolls and breaks up freely, but when you`re building a board thats tough to do with just a carving knife and a piece of foam. An easy way to add gentle rolling contours to your board while still retaining playability is to use `terrain goop`.
The stuff is a mix of pollyfilla cellulose based plaster, latex caulking, glue, vermiculite and latex paint. 
I think the importance of the celluslose plater and the caulking is to provide a medium that is resistant to shrinking as it dries, otherwise you`ll have some corrective work to do. I think this because I just made a batch without the caulking and it shrank up a bit and left cracks. easy to cover with some flocking, but I would have preferred a nicer finish.
Vermiculite is a product you can find in the hardware store in the garden supply section. Its a soil additive that will add texture to the mix.
The glue holds it all together, as you might guess.
As far as mixing proportions go, I dont use a specific formula, just mix it up until it makes a thick paste. I find it stays in place better when its thick, but  if you`re using it a a crack filler a thin mix might be better.
Just smear the stuff around. Instant ground detail. Very nice.

This used to be in my old blog, but its somehow disappeared...
A couple brief ideas that I use to save big bucks on my own terrain. Bear in mind I build for a class of kids as well as my own uses.

Go to construction sites for foam. Its expensive to buy, but also to throw away, so builders will give it away no problem. look for high rises and re-roofing jobs on commercial buildings, thats where they use it mostly.
And for cheap paint, go to the paint store and look at the mistints. A gallon goes for maybe $5. Super deal. And if thats not cheap enough, go to the paint recycling bin nearby. Talk about getting something for nothing...