Takes me back to the days of drafting, and sheet metal development.
Much of it boils down to bend allowances. Sheet metal (plastics, etc...) stretches on the outer part of the bend, and compresses on inner bends. Minimum corner radii are determined by the material's malleability. It's also about understanding the concept of "true shape and size" when it comes to working with angles, and compound angles. (In manual drafting, the concept is known as "projection").
For simple stuff, check this out:
https://www.smlease.com/calculator/sheetmetal/sheet-metal-flat-pattern-calculator/
For more elaborate developments, you may want to try Inventor or some other solids modeling program that has sheet metal development capabilities.
JB