the illustrated embodiment the unit is formed by cutting out the center and folding the bottom drip flange 108 and a top window enclosing flange 110 from the unitary sheet side portions 112 114 are formed of separate fold and metal pieces which are pushed through the opening from behind and welded brazed or are otherwise sealingly attached to the rest of the unitary sheet 106 at least along an attachment flange 116 provided on each metal piece a portion 118 of the upper window and casing portion 110 is folded around behind the two side extension pieces 116 provided 112 114 and is folded back on itself to interlock this configuration provides a dressed appearance similar to that which is provided by the embodiment using four pieces described above when completed as with an added embodiment in this one also a sealant can be used between the piece 106 and the window 92 such as the adhesive foam tape described above for example with reference now to fig1 and 13 in the case where the exterior treatment comprises stone work 119 a flashing 120 can be configured to direct moisture outward and over the stone work by means of a drip flange 122 similar to that described above.