How do I learn how to estimate repair cost?

[Patrick Philip]

I have the money to start another mass mailing campaign, but my sticking point is that I don't know how to accurately estimate repair cost. Where do I get started in learning how to do this?

At this point, I'm not even sure I can look at a house and tell what it needs. I have never rehabbed a house so I don't necessarily know what a contractor would want to do to it, other than obvious stuff like a new roof and paint or replacing old cabinets.