I just Googled FicamW and several sites came up.
FicamW is effective but dangerous to human and animal health so take precautions. Used with care, it will certainly sort it out for you, but be sure to pen the poultry well away from the shed, start early on a fine day to give it plenty of time to dry off, and clear out and burn any bedding or disposable dirty rubbish and scrub down the inside, perches etc back to the original clean surfaces before you start. If possible, remove the perches and pay attention to the ends where they fix into the sides of the shed. Wear a suitable mask which protects you from airborne insecticide particles, also rubber gloves, boots and coveralls. Spray carefully and leave it to dry out for as long as possible. This will clear the infestation from all accessible surfaces, but if the shed has roofing felt over a plywood layer, the mites will have crept in between the layers and the only way to deal with them will be to remove and burn the roof, replacing it preferably with single-layer corrugated material such as Onduline.
Do let us know how you get on.
