For a south-facing roof without storage, I find 30% quite decent. The problem is that it generates electricity around midday during the bright season, but most consumption is rather in the evenings and in winter. With your O/W roof, you will have better initial conditions because electricity is generated throughout the day. And with the business downstairs, you also have consumption all day long. Although that probably consumes a bit more electricity than a private household and, as a result, self-sufficiency may decrease ;)