Sandstone outhouse rescue

[apprentice builder]

Hi Guys
I live in a 125 year old tenement built from sandstone.
At the rear of the building there is an old washhouse that has no roof and is crumbling due to water ingress on the lime mortar etc.
I am going to try removing the damaged stones, failed mortar etc and saving the building
Not sure if you guys can offer any advice or maybe just say a prayer and wish me luck...
Either way here's some pics of the story so far -

 

[CzDuck]

It looks very similar to an outhouse we rescued at my parent's house when I was in college. Should be a relatively straightforward resurrection.

That said, it looks like that wooden beam has suffered fire damage in the past. I'm not sure if it used to be part of the roof structure or is only there to "keep the walls apart" but if you are planning to retain it (not replace it) and are thinking of using it for anything structural I'd want to double check it's structurally sound for the weight of a roof plus snow, wind loads, etc.