Look at national trust sites, Calke Abbey near Derby is a beautiful building and some areas of the property are yet to be restored, cracks in the walls, peeling paper, worn flooring etc. Attingham park in Shrewsbury has a lot of derelict garden buildings with all the old equipment in them as well.
There's Seighford Hall, the caretaker of the building lives around the back of the property, you could ask nicely for a tour. Also in Seighford you have the old RAF buildings if you don't mind braving the cattle, I believe they are owned by the farmer at Hexatall Farm in Ranton so, it might not hurt to ask first. And the estate there have some empty barns awaiting renovation.
The Hand and Cleaver is sitting empty as well, it's a mess from the outside, it's on the market at the moment, the owner is David Gough, he has a landscaping business so you could Google him for the number or contact the estate agents.
Good luck