what to do in what order

Rachiee

My Bathroom is falling apart!

I have had since purchasing the property issues with damp. The original flat roof above the bathroom.was very thin and inadequately felted and tarred and leaked. There is no window leading externally in the bathroom so ventilation had been an issue causing serious damp in the corner of the ceiling above the shower. There was a small extractor fan but that has been broken about three years now.Exasperating the damp problem.
Two years ago i got the roof re felted and re tarred however it seems to still leak over the shower switch after the recent heavy rain the turning on the switch (its a ceiling switch) causes the shower to trip.
Im worried that between the damp and leaky roof the ceiling of the bathroom has completely rotted and needs replacing but at the moment right now we cant shower.
We also have separate to this a very strong sewerage smell coming from the toilet not sure if this is caused by a leaky base or ground water coming up as there has been pooling where the pipes for the sink around too and I know the neighbours had a similar issue.
So here are the issues
1.Shower switch tripping
2.Possible Leak above shower switch
3.Rotten and damp ceiling with holes above the shower and cracks beside the shower switch.
4.no ventilation
5. Sewage smell unsure if this is from leaky base, blocked shower tray or ground water coming up under the tiles.

So who do I call first ? The electrician the roofer the plasterer or the plumber ! I have a lodger so I have a responsibility to ensure the shower works. Any advise appreciated.

shower switch

BryanF

Roofer & plumber first.