The Natural Philosopher wrote
R D S wrote

I know of a building which has been gutted by fire, stone and brick construction.

It was empty for ages before the fire and I had my eye on it coming up for sale as it would be perfect for my needs.

Most buildings in this state seem to end up demolished, it would need new floors and a roof but other than that is
there any reason why it couldn't be usable?

Not at all.

BILs house was reduced to a similar state, sold and rebuilt nicely.

It will also need insulation to modern standards - and its that *sort* opf issue that often leads to complete
demolition - the cost
of upgrading old stuff to new standards exceeds a demo/rebuild.

And a demo/rebuild is a lot easier to do too when the cost is similar
and you arent contrained by the original 'design'

Things that may catch you ou are

damp proof courses - there? sound?
subsidence and general foundation issues - underpinning aint worth it on a derelict.
insulation and windows - will it be simple to bring it up to spec? or
costly with special hand work needed.
Overall drainage and rainwater dispoal - are there good working drains
where you want them? Soakaway?
In the end commercial (comopany) rebuilds opt for the 'known cost' of
a new build rather than the risk of the restoration and that also
tends to need more intelligence on site. And they get VAT back too.