There are a few different types of bird and nesting boxes, I’ve outlined them below.
Classic style bird box
A classic style bird box is made of wood and has a slanted roof to help the water run off. You can buy slightly different sized ones, the main difference being that the hole in the front is available in different diameters.
25mm for blue, coal and marsh tits
28mm for great tits, tree sparrows and pied flycatchers
32mm for house sparrows and nuthatches
45mm for starlings
These bird boxes also have a little hole in the back to enable you to hang it easily to the surface you choose.