If you have a cloud of bats the chances are strong that they are roosting nearby. All bats are protected by law, and you commit a criminal offence if you disturb or destroy their roosting site, or do anything to stop or hinder their access to it.
Keep you fingers crossed that they haven't decided to occupy your roof space.
Birmingham City council in conjunction with other bodies did a bat survey in 2006, and still might be involved in bat conservation projects. Perhaps worth contacting them for more information and advice?.
Remember, even handling bats in the UK can lead to possible prosecution unless you are qualified-trained and have an appropriate licence. Its surprising how some people never know about bat roosts in their area, until they catch the odd sightings or read of a possible demolition that a find as been made.
If you want to see and photograph some big bat roosts outside the UK, then perhaps Batu Caves just outside Kuala Lumpur might be a starting point?.
If I was considering a loft conversion to my house and it just so happened that bats had decided to make their homes in the attic [all hypothetical], would I then be unable to go ahead with the improvement(s) to my house because of the flying furry creatures?
I have a few bats flying around at my stables for years, never managed to find where they come from. I think they must have a roost in a hollow tree or in some old WW2 air defence bunkers in the woods out the back. Been there all the time I have had the stables - last 30 years.