If you have a spare shed, move them, and creosote it! Failing that its its very hard to completely get rid of them, They live in the crevices and come out at night to feed off the hens whilst perching, thick cream ie sudocrem or washing up liquid squirted on the ends of the perches each evening helps prevent them feeding, diatom earth is supposed to be very good, also steam cleaning the shed every week. We had them and never completely got rid, so we got a upvc shed! the other is now creosoted and used as a spare or broody shed.