Timber frame side of house build

Hi, iv got a 5 inch concrete slab down the side of my house leading to the back garden, which I’m looking to build a timber frame room down the side, with no access into my house but using external house wall as third wall in the frame.

The slab is 5 inch thick x1900mm x 5000mm

Have attached a photo of my house and a photo of what the “plan”
Is