Scrap material mostly. I have some pine, cedar, mahogany and Ipe or iron wood.
Kind of like the last two on this page http://www.birdhouses101.com/birdhouse-design-variations.asp
Just to have some stuff to do with my kids...if it rains.
And to give to someone who does not expect it.
Nothing compared to our resident guru Cranbrook. Look his up in the galleries, you will be amazed.