d/stairs toilet to upstairs - drainage prob!

[LeeUK]

Soon to be moving into a house that has a downstairs loo

the house has a ground floor extention (L shape) with the toilet at the far end

I want to move the loo upstairs directly above the extention but the waste is to the far end of the extention and inside!
there is also an outside loo a little further on where i presume the indoor waste goes to

is it an easy job (obviously will be for a builder)
I have done most jobs myself before (plumbing, stud walling etc)
what is the done thing here when placing new inground waste pipes

any help appreciated

 

[LeeUK]

also, will i need to tell the council