Hey the easiest layout is just a small oval. It's 2 feet wide and 3 to 5 feet long.
If you can squeeze in a crossing you can make a figure eight that will make a good break-in track for new loco's too. For example I noticed the Doodlebug I got a while ago was quite noisy, the driveshaft from motor to truck seems to be the culprit. Once I built the figure eight for break-in, it allowed the loco to go around turns in both directions with out a fuss. This seemed to help a bit, as well as helping smooth out the operation. The loco tended to slow down more in one turn than the other.
Have fun,
Charles
Here is a link to mad Mikes layouts.... should give you lots of ideas.
Jim
http://www.naisp.net/mfischer/m_train2.htm