What is a good adwords conversion rate for a tradesman such as a roofer or a plumber?

[David]

It is going to depend on the page massively and the search term. Where is the incentive to fill in this form - to contact a trader? Do they get a discount.

I have very little idea but I am guessing 50% would be good if your page and service is what people are exactly looking for and about 10% if it is not that relevant. You need to split test and see.

Hope that helps - remember people will want a reason to fill in that form.