Constructing points motors for model railways

Has anyone built point motors for model railways? These are simply solenoids operating on 12vdc or 5vdc. I thought of using plastic tubes from ball pens (the outer tube not the ink tube) to wind the wire on but I don't know how to calculate the wire thickness or the number of turns on say for example a coil former of 9mm outside dimension. The solenoid would need to move about between 5mm and 1 cm. Would be grateful for any advice.

Jaycar catalogue numbers SS0900 - SS0903 are miniature 12v solenoids, but that depends if you have a set budget or would rather create them yourself, but on that, i cannot help.