Does he live inside? Are you talking about outside? A steel shed, unless air conditioned, will be way too hot in most climates. Those things heat up badly once the sun comes up. My family uses them to store tools and lawn mowers and stuff and some days it feels like walking into an oven to get something out of it. If you must house him outdoors, something wooden with windows or a/c would be better. Or just an outdoor area with predator protection and hidey holes, rather than an enclosed bunny house. But, again, many climates are way too hot for outdoor housing. Rabbits are very sensitive to heat.
Free range is something bunnies can only do after age and training is complete, no rabbit can just put into free range and do well with it. You have to gradually increase their space, or their litter training will be impossible. My suggestions would be a NIC condo (cheap solution that has many customization features and can be multi level for lots of space to run around) indoors with an x-pen you can attach to it for run time and work on litter training that way. He’ll have ample room to run that way while you work with him.
Also, a few common mistakes people make when litter training bunnies:
Intact rabbits hormones often make litter training impossible. Neutering/spaying helps in training, also it reduces smell a lot.
While litter training, rabbits need to be confined. The more space, the more they will mark and not use the box. Space should be gradually worked up to, not given all at once.
While litter training, multiple litter boxes can be used. You want to place them in the areas THEY choose and not try to force them to use the area YOU chose. So, if you notice the bun poops in one area more than another, move the litter box. Some members have even said they’ve lined the entire cage with litter boxes for particularly stubborn rabbits. Be creative and try to manipulate the rabbits natural instincts if you can.
While litter training, no soft surfaces should be provided EXCEPT the litter in the litter box. No blankets, no bedding in the bottom of the cage. It just confuses them.
While litter training, it is important to clean every accident up with vinegar to remove the smell. If it smells like a litter box, it’s going to be used as a litter box.