I'll agree with Gerry: Lemax units are reliable, work well, and are reasonably priced.
Also, if you want an operating roller coaster, get one that is already assembled. The increased reliability and lack of frustration is well worth the extra money. Spend it and lower your blood pressure! BTW: For wooden roller coasters, CD offers 2 designs, each has the same length of track. The more popular on is a twice around, which uses less space. The other is an out-and-back. Both are fun to watch! They have lots of other amusement rides as well. Check out their website.
Chris
LVHR