Im from Ireland aswell=]
Anyways i have 12 hens and two roosters in possibly an area a bit bigger than yours. Theyve been there for the last three years ( were free ranging before hand but the fox got hungry ) and its fine^^ in my experience if there is nothing in the run it wont last at all. But the run they are in now has multiple trees and shrubs, aswell as rotting pieces of wood which attract many insects. Its like a house in my view. If there were no internal walls it wouldnt last anyone any length of time as it would all be a mess. But if you add a wall or two, such as trees then it will last. I dunno, i just confused myself:x also throwing them the old vegetables in at different places will bring them to new parts of the run, which hopefully they will want to disvover.