I told em so - Damp in outbuilding

[yorky81]

hi first post but have used the site for advice and ideas for a while now.
just looked at a job where the client has had a builder erect an outbuilding in the back yard last summer and its has quite bad damp .
its a single skin block work wall rendered inside and out on a concrete slab. the trouble seems to be that it is built right up to the boundary of nextdoor at the back whos garden is about 400m higher than floor level and the rhs of the building is up against her garage with a gap of about 40mm which is full of mortar etc again about 400mm above slab level.
client says that the builder didnt want to build up to the boundry or the garage but she insisted as didnt want to lose any land ?
i am thinking of laying a visqueen type barrier on top of existing floor and bringing it up the internal walls above the outside ground levels and fixing with batons. was then thinking either a flagged or screed floor on top of this.
does anyone think this will be ok.
client is arguing with original builder but they are saying that she caused the problem so she can fix it. dont want to get stuck in the middle of em so should i wait till dispute is settled
thanks andy

[msh paving]

dont get involved putting there problems right till the have sorted out what they are gonna do as you could soon end up out of pocket MSH

[rab1]

run away as msh said you`ll only end up out of pocket. ???

[yorky81]

cheers guys
that was my gut instinct