This is a very easy project to make for attracting bluebirds to your yard. I wanted to reuse some of the wood I have from with the pallets I broke apart last year. This project uses a combination of industrial strength pallets made from 2x6s and standard pallets which provide slats in the 3/8" to 1/2" thick range. As for the house, I tried to hit the basic bluebird birdhouse dimensions for this build:

Hole Entry Size: 1.5"
Hole Distance Above Floor: 6" to 7"
Floor Dimensions: 4"x 4" to 5" x 5"

Feel free to leave the birdhouse exterior to weather unfinished or stain/paint it. I finished the house with a combination of stain for the bottom and sides and green paint for the roof.

Step 1: Tools/Materials

Tool:

Circular Saw
Jig Saw
Drill
Hole Saw (1.5" Diameter)
Drill Bits
Tape Measure
Pencil
French Curve or Compass
Hammer

Materials:

Pallet Wood - 5.5" x 26" x 1.5" Thick
Pallet Wood - 3.5" x 20" x 3/8" Thick (x5)
Nails
Eye Hook (x2)
Rope (1/4" x 30" Long)
Paint/Stain (optional)

Step 2: Drawing

You will be building to this drawing. The parts are color coded for easy reference.

Step 3: Front

I used a circular saw to cut the pallet wood down to 5" x 10". I next measured off 1.5" from the bottom and the center point at the top (2.5" over). These are used for the reference points for my profile. As for the profile, the design is really up to you. I used a French Curve to to get my profile. Below is a simplified version that can be made using a compass. Note that the bottom will be 1.5" thick so you should leave that section straight. Mark the profile onto the board.

I used a jig saw to cut along the marked line. This gives you the overall shape of the birdhouse.

Next, mark a location at the center of the profile up 7.5" from the bottom. Use a 1.5" hole saw or Forstner Bit to make the opening.

Step 4: Back

The back is the same as the front except no entry hole.

Step 5: Bottom

The bottom is 5" x 5" and is also made from the 1.5" thick pallet wood.

Step 6: Roof Slats

I wanted the bottom removable so I could clean out nest at the end of the season. Therefore, I only clamped it in for now. This allowed the bottom to line up with the sides when attaching the roof.

You will need to adjust the width of the roof slats as needed. I started with 1" wide slats. Since I did an overlap at the top, the house was no longer symmetrical. With this, I adjusted the slat on the other side to make up the difference. You can either screw or nail these on. I started with a hammer and nails but jumped to the nail gun after a while.