understanding surface sketches

these photographs show the corner of bedroom 1, all marked surfaces are insulated. Note slope L and the continuation slope K inside the cupboard. Note the gable end wall both inside the cupboard B and to the left C. The cheek is marked A. The wall to the rear of the property is marked F which is a continuation of E under the window D. The ceiling is insulated in three sections G, H and J, according to the actual construction above the plasterboard. Please compare these letters to the bedroom 1 sketch which is repeated below for clarity. All will become clear see sketch below the photographs.