The best thing about this is that you can make it as simple or as elaborate as your artistic skills allow (as you can see mine are somewhat limited!) and all you really need is an old roll of wallpaper, a pen and some toy cars.
I simply rolled out the paper and used blue tac to stick it down to the sides of the coffee table. Then to make sure I had a good sized (and even) road I used more blue tac to stick 2 pencils to the each side of a larger car and traced my road before going over it with a marker pen. As I did this the monsters gathered up cars and small world people and discussed what their 'town' would have...
It was going to have everything you could expect from a town, a police station, a post office, families with prams, horses in fields, a train station and even road works!
Together we set up the town and eventually it was ready...complete with dinosaur crossing!
At one point they used books to build houses, wooden blocks to build bridges. This kept the monster busy for so much longer than I thought it would! There was little arguing and some great imaginative play went on, what more could I ask for on a rainy chicken pox fuelled kinda day!