I've always wanted a secret door in my house. They are available to buy, but are $700+, which is WAY too much money, so I decided to try and build one myself.
I live in an apartment, and I didn't want to build an entire door I had to install. I wanted it to be something I could easily take with me when I move, so I built a frame to hang over my existing door.
I don't have any previous experience building anything, but it really wasn't that bad. I just made the measurements, went to home depot, found very thin, light wood, had them cut it for me, and nailed it together at home. The books took the most time. I had to take all the pages out, which took A WHILE. Then cut the books so it was basically just the spine and a little bit of the cover and back. I then super-glued all the books onto the shelf frame. The only ones I didn't glue are covering the doorknob (you'll see in the pictures).
Total cost was about $45-$55. Took a while, but it was a lot of fun, and now I have a secret frickin' door going up to our finished attic (This was about a year ago, which is why the Christmas tree is in the corner of the picture.)