This is a simple open fronted bird nesting box for small to medium sized birds such as song thrushes, (European) robins, wrens and flycatchers. I was going to publish an Instructable to make a box for hole-nesting birds, but Cheapchuck has done such a good job HERE, I'm going to make a few of his.
Some birds which were once common are declining with the loss of habitat and changes in climate, and gardens are a valuable refuge. Wild birds are very entertaining to watch and any effort to attract them to the garden and help them to breed is well worthwhile.
You also have the added benefits of free pest control. Birds, especially during the breeding season, will hunt down and eat many garden pests. It has to be better to encourage a natural balance of wildlife in your garden than to upset the eco-system by spraying with pesticides.
Step 1: Tools and Materials
I used a piece of rough pressure treated timber which had been at the back of my shed for many years. If you are buying new, use plain timber. It won't last as long as treated timber, but recently treated wood can harm the birds you're trying to help. Building the box took me a bit over an hour and that included designing it, so with a bit of effort, you could make a few in an afternoon.