This could be easy if two modifications can be made without too much effort.

1. Inside the closet there is a door casing that covers the gap between the door jamb and wall. You will need to remove this which would be taking a razor and cutting the paint in the corners, then a pry-bar. You will have to cover that gap though to protect the snakes. Use something thin like contact paper or plastic sheeting.

2. On the door jamb there is a door stop that the door closes against. Hopefully that is separate from the jamb and can be removed. Sometimes it is a double-rabbit jamb so you cannot remove it (See 2.1. for a solution).

2.1. If you can't remove the door stop, go to Home Depot (Or local hardware store that sells moulding) and buy 17ft of door stop (2x 7ft and 1x 3ft, or measure exactly what you need before hand and cut it there). There are two thicknesses of door stop, 1/4" and 3/8", so make sure you check what you have before you go. Apply this door stop so it is flush with the inside of the closet wall.

3. Cut shelves that will fit the closet tightly. Use 1x2's on the sides and back as a shelf "bracket".

4. There are many ways to build the doors. You will either install them on the door jamb if you removed the door stops or on the door stops you added.