I made a couple of alterations to the plans to make it look better and be more functional should any birds decide to make it their home.
The plans call for the sides to be made with small 1/4" strips cut from a 3/4" board, and be attached to the front and back panels. I decided to make a rabbet on the inner edges of the front and back panels and attach the strips there so they would not show at the front. I then coated the sides with wood filler and sanded them so that they are smoother and each individual strip would not show. A coat of oil based primer, two coats of colour, followed by three coats of clear finish should provide adequate protection. My dear wife did the colour part.
I also left space at the top of each side under the eaves and drilled three holes in the back for ventilation. One top panel is attached with screws to allow for cleaning. None of this was called for in the plans so maybe it wasn't intended for use as an actual bird house.
Whether it is ever used or not, it adds colour to the yard and the missus is happy.
Have fun.
John