Brilliant
Would love to do this, Poss a bit late now.
Do you have a parts list
There are a few pictures of the build on the first page. I will put together a list with some links as a few people have asked.
It will be too late for this year now but never too early to start for next year. Many species will start looking for places to nest in Spring 2021 from August - October onward. Ideally if you're going to put a box up it needs to go up by the end of summer to give them time to check it out and become comfortable with it ahead of next spring.
You never know though some birds have three broods with the last being in August so its still possible but it is unlikely.
If you can get it up by the end of the summer they may also use it to sleep over winter which is also very interesting to watch.