This picture is what your outcome should look like.

I've always wanted a bookcase that was secretly a door, and it's actually surprisingly easy to build. But unlike the movies, this design isn't controlled by pulling a book, instead just simply pushing it. To buy one of these would be around 700 dollars! So this is way cheaper.(Also, feel free to use any other type of wood, but plywood would be cheapest) Here's what you'll need for a 32 x 80 in. doorway:

Total average cost: $80

backboard- 32 in. by 80 in. piece of plywood
Shelves- 5 pieces of plywood, length varies depending on how thick your sides are, but around 30 inches long, 10 inches wide
2 door hinges
a pry-bar, or hammer
for sides of bookcase-12 in. wide, 80 in. long
extra plywood, or scrap wood
Screws and a screw driver
Wood glue or silicone
Books
Awesomeness

Step 1: Remove the Original Door

First, remove your original door. Unscrew the hinges and strike plate(s). Then, with a prybar, get rid of the inside door stopper at the top and sides, like in the photo.

Step 2: Frame

Now, to make the framing, first start with the two sides of the bookcase, 80 inches long.
Take one of your shelves and apply wood glue to the edges of it. Let it dry for around 10 minutes. Then just screw it in with your drill. Pretty easy, huh? It's basic. I used silicone for this, and you can too if you want.

Step 3:

To press in the back, line the edges of the case with glue and drill that on as well!
Remember to drill in the parts of the shelves too, for reinforcements. You can use a stapler after the screws, if you want an even stronger bookcase.

Step 4:

Now, since the bookcase is just plywood, it doesn't weigh that much, but if you used a heavier wood, you'll have to use stronger, longer hinges for it. Put down a piece of scrap wood before putting on the bookcase, so it won't get stuck to the floor, and that way it'll lift off the ground a little bit. Screw the hinges on the frontal part of the sides, so it can actually open. Remember to screw them on the inside of the doorway's jamb.

Step 5: Push It Open!

So you're done! Also, to make it camouflage in, decorate the walls around it to match the bookcase. You can even install more 'cases if you want. Just push it open, since there's no strike plates or handles. What's on the other side is up to you.

See look I'm pushing the door! :)