UpdateThe research & development side of my brain has overwhelmed the practical financial side and I have started work on a more elegant version of this roll-able BOC screen design.
So far I have acquired some select pine boards. I was happy to find you can get 1x3 select pine in 10 foot lengths. After picking through the entire stock at my local Home Depot I found 5 suitably straight boards. 4 of them for the top and bottom sandwich bars and one to cut in half to make the side bars from.
I discovered that the largest radius rounding bit I have is 1/2". I also discovered that to get a larger radius bit I would have to get a router that has a 1/2" collet. So I settled for the 1/2" radius for now.
So far I have cut the top and bottom bars down to 9' and put a 1/2" radius on the outside corners of the bottom bar. I also put the 1/2 radius on the bottom corners of the top bar even though they are not needed. I did not extend the 1/2 radius all the way to the ends of the bars. I wanted to leave an area at the ends with flat surfaces to accommodate the side bars.
I also routered a small detail on all the other corners. It is my intention to paint the bars matte black and then paint the corner detail metallic gold. I will try to use all brass hardware and I am hoping the gold will go with the brass to give a more elegant look to the whole thing.
I had some vinyl material hanging from the strapping version of the top bar so I attached the rounded bottom bar. The vinyl was worse than the BOC at retaining lines from being rolled up, so I figured this would be a good test. The rounded corners definitely makes a big difference. There are no apparent lines in the material when rolled down.
So now I have to find an attractive way to seat the side bars, and hold the screen in the rolled up position. I am also looking for suitable material to use for the 2.39:1 masking, and figure out a way to hold it in position with a nice straight edge.
Before I Forget . . .I have not abandoned the traditional idea of a roller to retract the screen. The idea of using a PVC plumbing pipe was suggested to me by Bud16425 (AVS member). I have looked at them and for some reason the white drainage pipes seem stiffer than the black plumbing pipe. You can get nice end caps for the pipe. I found the 4" pipe seems to be very stiff and that is what I would try using. You could drill a hole in the center of the caps and install a bold as the axle pins.
I say I have not abandoned this idea but I should point out that I have not found a readily available material that would be suitable for simple retractable screen design. I think this top roller design could be combined with the tab-tension side bar idea but I'm not sure what will be gained by using the top roller. In fact the whole thing would be bigger and probably less attractive. If you were going to hide it all in the ceiling there is some advantage to it though.
Better Tab DevelopmentI stopped into a fabric store on the way home from work and found some interesting things to play with. First thing I noticed were those iron on patches. There were the usual blue jean type and some very thin nylon ones. They had some 2x3" packs of 10 in the blue jean type that I grabbed. I also found some nice black elastic that looked about the right width for stapling.

First I tried simply folding the elastic over the edge of the BOC and stapling it in place (right tab). Then I cut a slit in the center of one of the iron on patches and folded it over the edge with the elastic coming through the slit. This resulted in a very finished looking tab but proved to be very stiff. I think it would be problematic when the screen was rolled up.
I went back to the V shaped tab to spread the thickness of the elastic out, (left tab). I then covered the elastic only on one side with an iron on patch. This was strong and much more flexible but I did not like the exposed staples on the back (shown bellow).

I tried to staple from the other side so the folded staple ends would be covered by the patch. The problem is you can't see where the elastic is and I kept missing and making a mess.
Finally I tried the V tab with a patch on both sides (Lighter blue bellow). It looks much better but is starting to get pretty stiff again. I think I may get some of the thinner nylon type patches and try them.

I am trying to develop fabrication methods that do not require a sewing machine and the skill to use it. If you have one and know how to use it then attaching the tabs should be quite easy for you. I would cut out round patches of the BOC and use the center slit idea to wrap them around the edge. Then sew them in place. This will hide the ends of the elastic and help to spread the tension out.
Masking MaterialThere was very nice clerk that showed me a lot of different materials that might be suitable for masking. I was looking for something inexpensive, not stretchy, and not shinny. I settled on a cotton material ( I will have to get the exact name). It is quite flat as you can see in the photo bellow. Much better at absorbing light than the matte black border on my screen.

I also found a way to use double sided carpet tape to make a very smooth straight fold-over edged. I will try making up a full width mask and attach it to the prototype setup I am playing with in the basement. I am optimistic that this approach to masking just might work. Since the masking is done with flaps that are part of the screen they roll up with it. Much easier to handle then long masking panels. The difficulty I see now is in how to place the edge properly when assembling the screen.