Would questions like the following be on topic (I made them up just now)?
What are some ways to pick the best roofing?
I know a lot of you mods will suggest this references the idea of a shopping question.
The second question is too localized, since certifications will be different in various parts of the world.
The other two are very broad, and may be difficult to answer. They seem to be wiki style questions, which I think are frowned upon by the community. They may also be closed as a duplicate of this question, which was asked in the early days of the community.
If you don't mind any possible reputation hits, you could ask them and see what the community thinks. I think they could be quite helpful to members of the community, if they get great high quality answers. Unfortunately, because of the way SE sites work. You'll likely end up with a ton of short answers, that future visitors will not want to spend the time reading through looking for the few gems of knowledge.
As for the third question, it might be more useful to ask about a specific product. For example. "I'm thinking about using product x. Is this the right product for my specific situation?".
Shopping questions can be on-topic, if they are asked the proper way. Questions like "What shingles should I buy?", are asking the community to do the research and tell you exactly what product to buy. Whereas "I'm getting ready to roof my house, what should I be looking at when shopping for shingles?", is asking the community to teach you how to shop for shingles, so you can make a more educated decision when you go shopping.
