A few years ago I built a approx 50X50 metal building on slab. Since I and my father and a friend did all the work I got it up for about 10,000 dollars. It is used as an aircraft hanger and is currently leased out since I live in a different state now. Here in my new place I decided I needed a new workshop for my airplane and various other projects. I called around and decided due to lack of time to just hire it out. My low bid for a 26X26 on slab and all wood with roof and siding to match the house and a 4 foot overhang on one side was 10,800 dollars. This includes 4 windows, 10' door and one steel hinged entrance door. It is being built off to one side of the house and is easily seen from the road. I wanted the structure to be airtight so I could heat and cool it. I love my big hanger back home but despite great care in construction it simply is not airtight. I built a climate controlled office with bathroom in one corner. Insects and other critters find there way in ---especially Dirt Daubers---!!!!. I had at my house back home, which I still own, a nice wooden 24X24 shop also built to match my house, it was so tight the door went k-thump and popped your ears when you closed it. No bugs and critters. It was airconditioned and heated with little expense. I built all kinds of stuff in there from an airplane to a hydroplane and was always comfortable.
My belief is that once you get much beyond 30X30 that metal will be noticeably cheaper but there are other factors to consider. Metal buildings are kinda ugly, even Mortans and will not match your house well. Huge buildings, metal or wood, cannot be heated or cooled easily. I will eventually put up a barn, approx 40X50 here also on the back 4 acres. I think it will be wooden also and will be built to have stone corners like the house. It will have a hay loft or upper storage area and will have a half slab. It will look like the classic local barns but just smaller. I will put electricty to it but I will not attempt to make it totally airtight nor will I cool it but I might put in some heat for any animals that I might decide to keep there. One other thing--just an observation/opinion, when you build with wood and stone you build for tommorow, when you build with metal you build for today.
Good luck with your building. J