This is what I usually work to:
Track length - usually on the shorter side, around 3-4km
Track width - around 12 metres -/+ 2m
Kerb width - 1 metre (concrete)
White line width - 0.2 metres (for visibility)
Pit exit line width - 0.3 metres (for visibility)
Pit lane length - between 250m and 300m
Pit fast lane width - 5 metres
Pit slow lane width - 5 metres
I have started using different shades of tarmac, to signify which areas are used more. Darker = standard config, lighter = less used / older config.
Pit exit at least 100m before turn 1, although for me, visibility of cars rejoining, and a gradual blend are more important than the actual distance.
Armco height is 1 metre, concrete pit wall height is 1.3 metres, tire height is 0.9 metres and thickness 2 metres, doubled up at the end of long straights or where required. Fence height (along pit wall, in front of grandstands, and some corners) is 3 metres. These dimensions are more for aesthetics and are not FIA regs.
My general rule for runoffs is as follows:
Depth up to 80m or more if at the end of a long straight, but I normally try to shrink it down to keep it more realistic, In my early designs I always added way to much runoff.
Majority of runoff is tarmac except for gravel deep into a large runoff. From the mid corner around to the exit, at the track edge I normally have 2m of grass, then 3m of gravel to keep cars within track limits. A 4m wide rejoining road is at the end of the runoff area.
In terms of FIA regulation, I think theres lots of info here: http://www.fia.com/circuit-safety
and a pdf for circuit drawing guidelines here: http://www.fia.com/circuit-list-requ...cuit-drawing-0
T1 hairpins: I use them sometimes, as long as they are quite open and not too slow (like Zandvoort or Daytona road, for example).
General notes on track design:
Working in 3D helps me a lot. It's great to be able to get down low, to really understand the flow of a circuit. Being able to put yourself on the track also helps with more logical barrier positioning, and other things like spectator sightlines etc. Adding elevation change is an easy way to add interest, but since I build all my circuits on a flat plane, I feel I have to make my circuits interesting enough that they don't need to have elevation change to be good circuits. This might be a weird concept, but its how I design circuits that I am happy with, within the limitations of SketchUp.
tldr; it's complicated
Feel free to ask questions if there is anything else...