It is important that nowhere edges / transitions form, on which the bats can get stuck with the claws.  

The gauze should be 1 to 2 mm mesh size so that the animals do not put the wings through the bars and can seriously injure themselves. The grid must be made of stainless steel, so that it does not rust through urine and is also stable and safe from rodents, cats and martens. For the same reason, care must be taken to ensure that loops, loops or loops do not form anywhere. 

The doors must be tightly closed. 

The walls should be slightly roughened so that the bats can climb. However, sharp edges must not be sharp so that the flying skins are not damaged. 

Please, see the legal regulations and the necessary official approvals for the construction and operation of a bat aviary. Aviaries serve only for the rehabilitation of injured bats. Bats are not pets! Wild animals belong in the wild. Once a bat is healthy, it must immediately be released.