You deffinately want some venilation not only for air flow in but also for stale air out you might consider a vent at both top ends of the shed one with a fan venting out, and you deffinately want windows for light you dont want a dark gloomy shed not good for buns outside, i have raised many buns outdoors thruout the yr summer thru winter and they were not in a shed but shelterd on a backside of a garage where the wind wouldnt hit them but also where they where there cages were mounted high enough up so the critters couldnt get to them and harm them even though bears could we never had problems with the bears they were always more after bird seed and garbage which we always kept cleaned up and put away befour dark. Our rabbit cages had hid boxes attached to the cage so they had a place to go out of the elements that we always padded down with lots straw the bottom of the cage was a wire wood mix so the bunnys feet wouldnt get hurt from being on wire 24-7 Durring the winter months we always feed a 18% protine pellet food so the buns had more carbs to burn per say. But we have always feed top qaulity feed anyways we have never used less quality just because it was cheaper, cheaper gets you nowhere and can make buns sick and weak. Durring times of hi heat if in a shed you need open doors and fans running to keep buns cool try not to have buns cages placed in direct sun, by the time winter rolls around you buns will have shed there summer fur in time for winter and have a much more thicker coat for winter if temps dip below zero you can always use a milkhouse little heater with a setting to keep the temp just to where its above freezing in there BUT make sure all hay and straw is picked up and cleared away from any heaters!!! Its also best to place heaters on bricks not wood floor.  In summer months when it gets to hot even with fans running you can use ice bottles in there cage to keep them cool they will lay against the bottle to cool there body temp down, we do this with large giant breeds durring summer months as they cant handle heat and handle cold way more better. If your cages are outside and not in a shed i sugest you get some tarps to wrap the cages in for wind and cold protection BUT leave the bottom open for airflow and poo droppings, They do have electric heated water bottles out now although i have not used one yet as they are expensive we have always gone outside several times a day and refreshed water to get rid of any ice build up and at night is when the water freezes thats when we use a bottle and also a crock partialy filled so that when it freezes if it does it wont crack the crock. Come morning we have the spare bottles filled with warmish water and switch everything out so buns can get plenty to drink and warm up. Make sure to supply plenty of good quality timothy/grass mix hay at all times. And poo that accumulates on wire bottoms must be scrapped off and or pushed thru the wire so buns are not stepping on it.  If useing a she please keep she clean at all times clear of cobwebs and spiders dont use chemicals around the rabbits if you need to debug the shed take rabbits cages and them out into a shadded area then spray down the shed and let air out for the day befour putting buns back watch for hornets and wasps as they are always attracked to shed door openings durring the summer and can sting buns badly and kill them.    Dont place bun cages directly infront of open windows durring winter even a closed window can create a bad draft so make sure to use some form of plastic of insulation over the window but make sure its clear for light to pass thru, bubble wrap makes great insulation for glass and or plexiglass windows. Main thing for cages in shed is to keep you litter/droppings pans clean scraped off atleast once a week and wash them with bleach water mix to disinfect them dry with paper towel,  in winter this can be harder to do so atleast once a week use a scrapper to scrape the poo and frozen pee off the tray/pan as clean as you can get it look for a good spray made for indoor rabbit litter boxes to spray the tray/pans with befour placing them back. Wash clean water bottles so they dont get algea slime build up.

Just my 2 cents worth……

This UK site has some good tips. It seems to be a popular way to house rabbits the UK, from what I gather.
http://www.therabbithouse.com/outdoor/rabbitshed.asp
http://www.therabbithouse.com/outdoor/insulating-shed.asp