Key Template

This is a standard key template. To make it fit into your own to door, you can import the model into e.g. Onshape and a picture of your key. Then you can draw the outline of the key and remove the material afterwards.
You can also use a file after you have printed the template key.

I printed it with 0.1 mm layer high and it worked as a functional key in my door.

Here is a video that goes more in depth: