well that is a complex system.
You would have to start small, and build it up more complex.
.....
it would have to check to see if the cursor has moved, from the original pos, to the left right, or up / down, and when if it gets past a certain point (the end of the first model) create another model, of the same type, until your script notices a change in left / right movement, then it would create a bend / curve..



I would suggest a menu, that allows you to select what road piece you want to use, and then you can click and place them. much much easier to start off with.