[Dwight]

you can use lite cardboard or heavy paper to make templates. Use masking tape to fill in the gap if you mark/cut it wrong. Lay them out on the carpet and mark, then cut. If you use a Sharpie for layout remember not to leave any ink on the finished carpet. I'm sure there is something out there that will remove it but I could not find it.

Find a carpet store that does edging or an upholstery shop.

It's not a hard project. If you have carpet and are just replacing it, that should be easy.

I did my floors, then the sides of the tunnel, with a piece on top of the tunnel. Glued everything down.
I bought my outdoor boat carpet at Lowes. Somedays it rains.
Have fun
Dwight