Thank you for your comments. With the pop top raised, there is room for two to lie down quite comfortably in the tent like space. A two part foam mattress (removable) is in there for a comfortable stretch. This space is in addition to the bed that is formed by pulling out the seat so the seat back and bottom are aligned horizontally.
The access to the sleeping area in the top is thru a hole in the roof. However as you would probably guess, there is more to it than just a hole cut in the roof. The roof is reinforced by metal sections and supports that are hidden out of sight. I am not saying that it cannot be done successfully here but I wouldn't want to attempt the hack job on a perfectly good solid roof. I have plans to utilize the space and allow for two people to sleep up there but the access to the space would be from the outside and not the inside as you see in the original Westfalias
The answer to your question therefore is that for now the pop-top is a mere decoration with the only possible function of keeping the main roof cooler by keeping the direct sun off. A solar panel is going to be fitted in the front quarter of the top to recharge the RV battery. This set-up is going to power all my lawn and gate lights at night when the bus is parked in the driveway. (more on that later)
