anyone know how the top of this prison is built?

[jstarscomm]

at time 0:15 how is the top part built. especially how they cover the top part in the middle with two bars.

[anothergol]

the roof looks like 1 part but it's probably the blur that makes lines disappear. Looks like a simple 4x6 plate with a row of plates on top for double thickness, to me