Mantel Units

[steptoe]

I'd also hazard a guess,

that there is a service 'void' type thing going on and all the 'mains' cables run straight up the middle of the building, where your mantel is,

moving this isnt going to be easy, to say the least,

 

[NozSpark]

Id go with that,,, I just can't see how they'd move it to the proposed location

 

[Blue Duck]

In your drawing the mantel looks pretty central, but usually the risers are on the stair wells with a ryefield type thing on each floor. Where's your neighbours mantel?

Looks like you will need a a structural engineer and a good electrician. All very expensive for what will be a very claustrophobic shower cubicle.

Also where are you going to run the waste from the shower if your floors are concrete this won't be easy either.

Good luck!