by placing a partition down the centre ,front to back ,small access door through .not beyond most as a small d.i.y. project .you say its brick built ,I would be tempted to put some air bricks in for ventilation .the door on the side could have a louvered bottom to help again .a single trap on the front .take a look on you-tube for some examples of how the Americans set up theyre small lofts . as for the stock you could keep the stock cocks in with the widowers and the stock hens in with the youngsters .however ,I wouldn't recommend keeping very many at all. like I said earlier ,anything is possible with a little thought .