Here is an English translation of an August 1942 plan for the bunker and pole support roof behind B41. The construction office referred to this project as Building XIIA. In this and other documents it is described as a disinfestation facility with delousing chambers. After the Germans left it became "gas chambers".
I think this is an effective way of showing that this place was built for a hygenic purpose. The roof's purpose was to air out clothing and other effects that went through disinfestation in the bunker. There are "clean" and "unclean" sides labelled. The crude arrows coming from the bathing barracks may indicate the flow of dirty clothing, since we know from the floorplan for barrack 42 that its north side was its unclean and undressing side.
Unfortunately the quality of the original image is poor. This is
Concentration Camp Majdanek's Document 31. If anyone has a better quality scan, that would be helpful.
Some of my labels may need correction. "Canopy" is an unlikely translation for what appears to be "zeil", which is for some reason written twice on the drawing. At center, "Detail of the concrete" is correct, but whatever word comes after it is indecipherable to me. Corrections welcome.