Building a garden room next to retaining wall on sloped garden

[Jordon93000]

I'd like to build a garden room, next to 2 retaining walls.

Now I was wondering if it is possible to incorporate the larger retaining wall in to the build, and use a timber frame for the remaining walls,

If not if I build next to the retaining wall, leaving a space, do I need to do anything specific re drainage etc to stop damp getting in the garden office?

 

[mattylad]

I'm no expert but I would probably be taking up the row of slabs in front of the wall (which is not looking too great) and digging down with a french drain (I think it's called that) where you have the gravel etc, then have that fed to the front of the patio area via a pipe dug down.