One of my friends has done this some years ago
You have to register with park rangers and if you are not back by a certain time they rescue whether you need rescuing or not. They bill you for the unafordable inflated expense.
Its more climbing than Ben Nevis, but you start at the top and have to come back up in a climate which is dehydrating and so you have to carry lots of water
If you are up for it, it must be a fanstastic experience. Possibly more info is on the internet. I hope you suceed, but think long and hard