This is an idea when you want to create some special lock using 1d8 and 1d4. In the image you can see the diagram how this works, it is very simple yet can add some intrigue and interest to your players at the moment your creating it.
Low DC lock gets harder to picklock after a failure. Add +2 to the DC
Complex DC can be tried several times without risk of increaasing the DC but after 3 failures the lock magically get unable to continue trying until 1 hour passes. you are the DM you can modify this as you need to.