Any outdoor hutch should provide your rabbit with sufficient protection from the weather. Depending on your location, your primary concern may be sun, rain, wind or snow. While all of these must be taken into consideration, each location will have its own challenges.
If you live in the north and get a lot of snow in the winter, you will want to find a plan with a reinforced roof. The roof should be slanted, allowing snow to slide off. The hutch should have enough solid walls to allow the rabbit a place to huddle to conserve body heat.
If your cage does not have several solid walls, you can put in a wooden or plastic house for your rabbit to hide in that will help them keep warm. Straw or hay can also be stuffed into the cage to help your rabbit stay warm.
If you get a lot of wind and rain, the slanted roof will still help. Make sure your hutch plans offer enough eaves around the edges of the roof to keep rain from blowing into the cage or dripping into the feed. The hutch should offer protection against the wind so the rabbit has a protected place to stay.
If sun is your primary problem, you will want a nice shady spot to situate your hutch. Make the eaves large enough to cast shadows over any openings into the hutch.
If you were thinking of a tin roof, you may want to rethink that option in a sunny location since metal can get very hot from the sun. That heat can radiate into your rabbit’s cage and keep him uncomfortably warm. Lots of air flow is imperative in hot weather. You may even want to set up fans to help move the air around your rabbit cages.