custom-made routes

Any basic GPS will do what you want eg:- Garmin Etrex 10 or 20, you would be creating a Track rather than a Route as a Route must follow a road or path already on the map, a Track is your own new path, it is stored in the GPS and can be followed again at a later date either by comparing your current on-screen position to the displayed Track or by using the compass screen where a pointer will show any turns needed to keep you on the Track, you won't get an audible 'Turn Left' type message as this is only supported on vehicle satnavs that follow a Route along a road