I would say that my sketches are usually for guidance. Like you my buildings grow organically, a bit like this project, I have already lengthened the building and started to work on a lighted furnace using a battery operated Tea Light.
I am also used to working to very strict commissions - where the details has to be very exact, (for example if building a master for resin casting) but when I build for myself, its just for fun.
I have kept most (if not all) of my sketches, they are rolled up in a cardboard tube in the attic!
If you are interested both of my books Building Wargame Terrain and More Wargame Terrain include sketches.
Regards and good luck with your Aerosled. I think it looks awesome.
Tony