Hoping for some advice on whether there is an option of just having a single skin wall located under a bifold door and not use a double skin cavity etc. This will be the outer wall with the usual inner hardcore, insulation and concrete slab being taken to this wall. 

You mean run the slab up to the outside wall..? Can be done but needs a decent insulation upstand to stop heat loss across the threshold. 

Thanks PeterW, yes  no cavity wall built from foundation just a concrete block outside wall with the slab constructed to this single skn

Any further advice out there would be appreciated, the builder has only done a single skin wall, is this ok or must it be a cavity, would be great to get some thoughts before the slab is filled in.

That's what I did but had decent insulation between slab and the outerleaf brickwork.

 

The bi-fold door frame then sat on the outerleaf wall, (one brick course removed so was 75mm lower) so the inside of the frame is pretty much flush with the finished floor level.

Thanks George, did you do 100mm below slab but nothing as an upstand just concrete to the outside skin with DPM etc, just trying to picture it.  You answered nother question on location of Bifold door being on outer skin although I have two 100mm square section posts in the cavity with an A Frame, wasnt sure how the head of the door was going to be fixed if the steel frame is sat back from outer skin