Here you have several tutorials on how to create MRO tracks:
http://www.miniracingonline.com/tutoriales.php. However, most of them are in Spanish, so you might have a hard time understanding them. Anyway, if you understand them (or if you google-translate them), I'm sure you'll find them very useful.
It turns out that circuits aren't really my thing, and I don't know about how to build them. However, there are several good designers around here, so why don't you try to contact people who have created actual MRO circuits and ask them for help?
Greetings from Gran Canaria, Spain.
