I like beds to be made tidy! May be bird specialists would disagree. I put a pre fabricated nest in. These are for sale in pet stores, but I made this one myself I made a 2 meter long cord by finger-crochet, coiled it up and sew it together with the same type of rope and a big weaving needle. May be more details in an other instructable. To secure the nest in the bird house i punched two hole in the bottom of the house end threaded a tie-wrap. A hole in the bottom of the house is a good idea, we don't want to make a birdpool. The overhanging roof will keep the rain out, but you can never be too sure.