Making downstairs loo n cupboard into a shower room n loo?

[butterscotch]

I wondered if anyone has done this and can give me. Rough idea of costs/any potential issues?

We have a 1960/70's chalet style house and two girls really need a second shower. We could put an ensuite in our room (big enough) however it's otherside from bathroom so I suspect this would be expensive! Other option is to extend into the spare room to have a bigger bathroom but knocking out the Downstairs cupboard and making that into a shower cubicle(moving downstairs cupboard to under stairs).

There is a small window that goes to the porch, we have pipes in the room because of toilet and sink....

I'm guessing we'd prob tile the whole room?

Has anyone done this before? Is there any building regs likely to stop us from being able to doing it?

I can bake cakes but diy is not my greatest strength!!! However I'd plan to buy suite etc... Happy to employee plumber/electrician/plasterer as individuals or use a company?

Thanks in advanced!

Thanks in advanced