intersecting and surface matching "creates skylight instead of making floor
I do not know why the floor and roof ceiling of my rest room on the plenum adjacent to it is skylight as this is sub surface and I can not manually match this skylight to floor or roof ceiling of my rest room like David has explained in this page 
I do not know how to fix it, Any advise or guidance would be greatly appreciated
Does this help? https://unmethours.com/question/2382/...
@Eric Ringold, Thank you so much, That was really helpful.
That was the same fix I was going to suggest. @Eric Ringold you might consider moving your comment to an answer :-)