If it involves charging for the use of self-propelled construction plant or hoisting machinery, most national health and safety authorities will require you to restrict usage to fully trained operators.
If you've already got to manually check their certification, simply take a deposit, record the hour meter reading before and after and bill for hours run. However you will find that canny users will shut off the engine whenever they pause for any reason which will put a heck of a lot of extra wear on it, so you might do better to simply charge for elapsed time.
It could be automated by fitting each machine with an electronic keycard reader instead of the ignition switch and having a machine that takes the user's credit card, checks that user is registered as trained and authorised, then releases the keycard. When the keycard is returned, it checks the machine is in its parking bay by RFID tag on the machine, checks hours used recorded on the keycard, bills accordingly and prints the receipt.