1) Easy to make with no special tools
2) Be at least 2 stories tall.
3) Make it look good enough to sit in our den
4) Make it for under $20
Step 1: Supplies and Tools
For construction I used some left over cardboard boxes I had laying around as well as some spare pieces of cardboard. I also I decided to dress up the outside to make it more presentable (optional) so I used craft foam for siding, foam board for trim and good thick poster board for shingles.
*Box Cutter or Xacto knife
*Good, sharp scissors
*Hot Glue gun and plenty of glue sticks
Step 2: Building the First Floor
Next, I cut a portion of the top flap out to give access to the second floor from inside (this proved mostly pointless as the cat just jumps into the second floor via the windows).
Because I was worried about structure I decided to construct a cardboard "beam" to hold the weight of the cat. I took a piece the same length as the width of the box and scored it at the following measurements:
I cut it off after the 1 1/2" section giving me a total width of 6 1/2" and folded along the score lines. I folded the 1 1/2" section under the first 2" section and hot glued those two sections together. What I was left with was a 1" X 2" beam that would span the width of the box right next to where the top flap was cut.
Then I assembled the box with duct tape. Make sure you put in the beam before you tape the top flaps shut so it's easier to install. To make sure the beam stayed I made 2 crude joist hangers out of duct tape the added more tape until it seemed secure when I pressed down in it. Then, I taped the top flaps closed.
Step 3: Building the Top Floor and Roof
For the second floor I cut the bottom flaps off the box, as well as the side top flaps. Then I measured out windows and cut them out the same as the door (size is up to you, mine were 6" X 10" I think). After cutting I duct taped the top floor onto the bottom floor. I would suggest taping outside and inside to avoid fur getting caught in the tape.
If you just tape up the top flaps you will get a flat roof which may work for you but I wanted a sloped roof. I didn't have any cardboard the width of the boxes I'd used for the two floors so I had to tape 2 pieces together. I added extra strips duct taped to the back to make sure it was rigid (as you'll see later this probably wasn't needed) and cut them to a length that gave me a nice pitch then tapped them on. I had left the long side top flaps on so I had something to attach them to. Then I used the roof as a guide to mark out and cut pieces to fill the gaps caused by the peak of the roof.
Thoughts about a flat roof:
Depending on what style you're looking for you could also get a good look from a flat roof. A more modern look or even if you wanted to go for a castle look you could just add cardboard battlements and give access to the roof the same as was done for the first to second floor.
Step 4: Making It Look Good
For siding I used the craft foam and cut it into strips (I just used the width of my straight edge). Using the hot glue gun I attached it one strip at a time leaving an over hang to make it look as much like real siding as I could. To make the revel even I started with a spacer but this took way too long. After doing the front I switched to marking out a grid to follow and the process went much quicker. I left the strips long on the edges and just went back with the scissors and trimmed them down when I was done with the side I was working on.
For this I used foam board because I wanted something more rigid. I cut it into strips just like the siding then attached it along the windows, door and the corners. I glued the boxes for the windows and door before attaching them so I could glue the joins together to hopefully give it more strength but in retrospect it didn't seem to make much of a difference and skipped that on the corner trim.
Because I had extra sheets of foam board I trimmed 2 pieces to size and attached them flat to the roof first. it gives the house the look of eve trim. Next I cut black poster board into strips. After I had it in strips I cut about 3/4 of the way through the strips width-wise to give them the look of a strip of shingles. I glued them into place and trimmed them down same as the siding but this time left a slight overhang like you'd see in a real house. Next I used my fingers to lift the "shingles" a bit then let them fall down, this helped give it a better look because the "shingles" looked more separated.
As an after thought I decided to give the cat something to play with in there and duct taped an piece of string to the underside of the roof.
Step 5: Final Thoughts
The project took a lot longer than I expected but only because I decided to use siding. If you were to just cover it with flat craft foam or fabric I would guess around a total of 2 hours to finish. The way I did it took about 5-6 hours.
If you were to cut out the back wall and add some room partitions you could easily turn this into an inexpensive doll house.
The cat didn't seem to care about the siding, I could have stopped with just the structure and she would have been just as happy. If you were to stop there I'd guess the project would have taken less than an hour.