I didn't plan on an instructable, so I didn't always take perfect photos during construction, but I will try to explain the best I can. I built what fits for my application, for that reason, I omitted exact measurements. The paneling was used due to it's light weight for the door, and I had a boatload to use up and can be seen in the Landspeeder instructable I did.
The door opening ended up being 81" tall by 56" wide.
The shelf depth is 11.5", and the capacity of the door 450lbs... which should be more than enough for most projects I imagine..
The area to the right is also a hidden door in that it accesses the under stair storage area, is the same material and doesn't have a handle. Its of a regular hinged design, so it's not anything special. however the entire wall together is a good effect.
Step 1: Figure out what you have to work with
This is the proof of concept photo.
The hardware used was National Hardware brand purchased from Tractor supply. the trucks and the rail itself came to around 100.