Not to brag or something but I done like 500+ lyts on au and other tracks.
So I hope I can give you some tips from what i learned. If you wanna build on au1 perfect track widnes is 10-12 meters(for touge tracks even 6-8).
First you need to get a rough pic in your head what u gonna make or what u wanna build. Then just go freehand , i prefer making a track with chalks only at start , so u get a track/lap marked with chalks only , then u measure all parts so its all symetric , then again its up to you because all u have to do is decorate it by your style or taste. Sry for my bad english , some old lyt makers will know what im talking and i hope i helped you some too with this post. Good luck!