Don’t query on half-written, almost written material. Query on completed projects. I know you’re impatient and eager to get published; the writing is coming along nicely or maybe not so nicely so you want to query to validate your own worth and work by hopefully getting a positive response to help goad you on for the rest of the way, but you have to have the work done to properly query. Who knows what will happen in the course of your writing you could hit a major snag (someone could die or get hurt, you go bankrupt, who knows!) and not be able to complete the project in the 2-3 weeks you may have promised the agent it would be completed in.
An incomplete project is too risky for an agent to consider if you’re not already published and have a good track record. Your job is to write the book; the agent’s job is to sell it.