[freebeard]

A rain cover should overhang the deck. Making the upper level a deck precludes getting light and ventilation into the main space. And it would require engineering for the stresses that pass over the top surface of the dome. From wind loads and such.

Consider the attached tower in Permalink#20 with vertical openings on the top level and a[n] hemispheric roof.

Which reminds me: Oregon Dome IIRC spent $1500 on the engineering that they used for each building they put up for decades.* For a skylight panel, they inset a smaller triangular opening in the standard panel. Which is framed with 2x4s ripped on the long edge.

If you rip a 4x4 in half and put triangular gussets in the angles, you'd get a full width hexagon opening.

*Making your own panels would involve using Fuller's Hexapent design for the engineering approval (and other advantages), a table saw that will rip a 4" cut**, and two chop saws with a clamp in between so you can cut both ends at once. And an assembly jig.

The raw materials, plywood and 2x4, were $1500 in 1980 and the kits sold for $6-7000.

**I have one (11" blade) but the motor needs to be rebuilt or replaced with a VFD induction motor.