I am in the process of building a Benesh profile Savonius using Picoturbine plans, it slow going with my other committments though (check out my diary to see what's going on)
Looking at that design it is similar to a Benesh, however it looks a good bit harder to construct due to the curve of the blades. What material were you thinking of using for the blades? How are you going to make the end pieces and attach the blade material to them?
I am using wire mesh and fibreglass, great fun but messy (I float out of my 'shop sometimes so watch the fumes
) I found it quite difficult to maintain the shape of the blade across the whole area. But I am getting it close enough for my first attempt.
Someone suggested that I use fibreglass sheets, on reflection this is a very good idea, but I wonder how much strength you would be able to achieve. My mill needs to stand up to some serious winds (>90mph last week) so I like my method, it seems very robust, time will tell though.
Something to consider is the fact that VAWT like to have a high aspect ratio (6:1 or 8:1) in other words tall and skinny, not short and fat. It would be better if you constructed more than one blade set, two would be the simplest (offset by 90 degs.) although I have seen 3 set VAWT's. You will be encountering the law of diminishing returns eventually though. My advice would be to keep it as simple as possible.
You would expect the mill to turn quite slowly, what are your thoughts on the PMA design? Big diameter disks with lots of magnets (high frequency) and coils with lots of turns (high voltage) would help you get the best from your mill, but that would depend on your budget.
I hope this helps.