I've never worked w/it nor seen it 'live'. BUT, I've seen it used from time to time on some of the various Home Shows on television. And from what I've seen, it looks pretty good. I don't know how hard it gets. In other words, can you walk on it w/o damaging it. I DO remember seeing a roof being installed one time where a membrane was first layed down, then a liquid was poured where it hardened. With this product, the homeowner was able to put deck furniture on it and use the roof as a deck. (Structurally, the roof was fine so they could do this. This type of roof didn't add anything to the roof's ability to hold weight.) It was white which allowed it to be reflective. Since it's white, it doesn't get hot either. Maybe the SPF is like that.
In the meantime, go to My Favorite WEB Search Engine and enter in +"sprayed polyurethane foam" +roof ('+' and '"' included), and press Search. You'll get an awful lot of hits on the subject. In the meantime, I'll see if I can find out anything more on the other product I mentioned.
My best to ya and hope this helps.
PS: The membrane and liquid product I saw was being used in the Southwest because of the heat issues ...