we cut a hole in the floor,roughly in the middle and just cover with fine mesh .size is up to you.ours is a ft sq.also easy to cover again with a board.
i know its not always possible but we built an avairy for the birds to have bath.If its results you are worried about,i know of a consistent national performing loft who s birds dont go out till nearly 3-4wks before racing starts.
Just wanted to say thanks to Tel and his wife,for making dad and myself welcome,letting us handle endless top class birds that really were in 1st class condition,all in all a top day and the set up and birds were a credit to you both,thanks again