If more than 2m high of the walls still exist for most the circumference - as far as I know you will need no planning as its purely repair work to an existing building.
If you are 'repairing' a building you can use any materials you like (within reason) - once you goto planning you will have to 'fit' in with what they think a building should look like.
If it effectively just the footprint of the building left then you will need planning as it will be a rebuild - to rebuild a barn you will have to prove you need a barn (under 28 days agri planning) - and dont use the word animal shelter - use the word 'food and tool storage'
If you plan to rebuild as a dwelling you will need full planning for everything, building, drainage, access etc etc
Whats the story - is the building surrounded by land you own? Is it a small parcel of land with a barn in the middle surrounded by other farms?
Hard to tell without more details.