10 years or so ago, the place I worked took part in Learning at Work Day. I trained people in juggling (Since I normally ran courses in web page creation, something a bit more interesting seemed in order) and then took the opportunity to have a go at building a robin box, run by one of the Park Rangers.
On the footsteps of Shire Hall in Warwick, we hammered together some bits of wood to make a suitable homes for our red breasted friends. I took this home like a child who'd made something at school, and screwed it to a fence post.
Over the years, a couple of birds have made the box their home but as the wood was never protected with varnish or preservative, the roof rotted away.
Anyway, the time had come to provide the birds with a new roof and as it happens there was an offcut of 9mm plywood left over from building Clayhanger Yard more than large enough for the job. A few minutes with a square, pencil and saw and I was able to nail the new lid back in place. I even varnished it with a couple of coats so it's a bit more rain-proof.