Just cleaned the roof on our Windjammer for the first time today. Haven't been able to use it because it was winter when we got it.
We used the Murphy's Oil Soap as per the owners information, etc. The roof didn't come really clean and there was still some bad stains on it that probably came from nearby trees blowing leaves, fuzzies, etc. We do have a cover to put on it to protect it now. Before it was in an outside storage yard away from our home and now it's here for safe keeping and looking after.
I contacted the Alpha System company(manufacturer of our roofing) to see what I could use that was better than the Murphy's. Got an immediate reply shortly after sending an e-mail. This is what I was told and I thought there may be others out there who were just as confused as we were as to exactly what was safe.
You can you household cleaners on your roof, just nothing abrasive. Products with bleach are ok as well. So the dawn is fine, you can also use Simple Green, or if you have sticky areas or sap you can use Goo Gone. Bleach in your cleaning solution is ok as long as you make sure to rinse well afterward.
If you have further questions, let me know.
Alpha Systems, LLC.