I think theres loads of regulations, for material specs etc, you need to get hold of the rules....
Then i suppose pick your engine box,n get out and have a look at some, check the club websites for inspiration...then start building stuff!
I have a Z-cars chassis class 8 using a suzuki bandit 1200 motor you are more than welcome to put a tape over, made from 25 x 25 x 3 box for the main chassis 50 x 25 for the trailing arm mounts and 50 x 50 x 3 box for the trailing arms. Why you want to go around in a circle all day beats me come over the bridge and give auto-cross a go probably 12/14 meetings a year not far from here.
That involve gawn round a circuit marked oot in a field. A sprint with four at a time around four heats then a dash with the fastest four at the end of the meeting.
No where near the M8 but on the A1 at Morpeth Causey park this is the club that organise the events www.ianhardy.net/autocross_calendar.php Border Ecosse also do a couple of events around the borders. May be worth your while having a look and pickup a few ideas.