216 cubic feet; you'll need some sort of internal frame with a means of hanging them up on to the rail just under 6foot inside, drip trays, preferably some means of drainage and preferably a smooth washable floor. If your fallow are decent weight, consider the lifting up of the carcasses carefully, a hoist boxed in above ceiling height aligned near the rail is preferable again, as there’s not a right lot of room for two grown men to lift up the last of the four on to the hooks which you’ll need for the rail. This also has implications for your ceiling strength unless you can fix it within the building out with the cold store and arrange a means to permit both the control wire and hoisting wire with hook to be passed down through the store ceiling.
PM me if you need strong ‘S’ Hooks, fit for the job and big enough to give you a fighting chance of managing to successfully get the gambrel on to the hook or the hook onto the rail, small hooks are a pita in that respect.