The "roof" was built out of sheet metal with black PVC pipes that could have the ends cut to make a good fit on the cube. Metal eletrical conduit provides support "bones" for the PVC to reduce bowing and add stability. There are cheaper and lighter ways to build a cube roof but I wanted metal because my plan was to use magnets to hold the ships up. This would give me the freedom to freely configure the ships anywhere in the space and provide the ability to adjust things like pitch and yaw of the ships with multiple supports.
Most of the materials came from home depot. I used neodymium magnets for their high pull-force to size ratio from Applied Magnets (www.magnet4less.com). I wanted to give the support threads the best chance of being invisible so for the background I chose black photography vinyl designed to reflect as little light as possible. In this case I used Savage Infinity vinyl from B&H (www.bhphotovideo.com).
The support threads themselves were a bit trickier. I wanted something that would be as invisible as possible but it had to be sturdy enough to withstand everything up to a minor earthquake (this is in Los Angeles after all). I tried all sorts of things from tungsten micro line used for floating props in photo shoots to magician's "invisible" thread. While I found some really good results in terms of visibility, none of them had the tensile strength I needed. In the end I used braided fishing superline, made in a black-ish color (www.berkley-fishing.com). I also added some computer modding LED light fixtures but the ambient light in the building makes their effect very weak.
I'm pretty happy with the end result of version 1. The building I work in has a lot of ambient light, including direct sunlight from some windows that I may want to take steps to control in version 2. I also might want to use some thinner line for the smaller/lighter ships to help decrease the support visibility. I opted not to add a starfield to the vinyl as I couldn't find a technique I liked enough. I also kinda like the museum or "installation" feel the pure black brings.