This project is intended to show how to actually use the typeRoots option of tsconfig. It is woefully underdocumented and difficult to remember how to do right.

The main issue is that setting typeRoots alone is not enough. You ALSO have to add/update the paths option of your tsconfig so that the file is actually found:

{
  "baseUrl": ".",
  "typeRoots": ["./node_modules/@types", "./custom-types"],
  "paths": {
    "*": ["*", "./custom-types/*"]
  }
}

The frustrating part is that you don't have to explicitly add ./node_modules/@types/* to the paths config.