Preset radius is easier to work with rather than flex track! 

Use a nail and a piece of string tied to pencil/marker, measure radius and draw center line. I have old curved track from old train sets from youth (brass). Good to use for templates also as you did.

good idea using set track curves so much easier than fiddling with flexi envious of your shed you have !!

Ok, so how about using the set curves to set up the radius, glue the roadbed in, then replace the set curves with the flex radius?

Where do you order your fixed radius track? How is it “forced” to maintain the exact radius?

👊