Time table for design of a room addition

My wife and I are looking to add a family room addition to our house (typical 1950\'s ranch in Old Leawood). We are hoping to do this early next summer (May/June 2008). Given that timeframe, when would be the right time to start getting bids from contractors and ultimately choose one to begin the design process?

Mark,

If you pick May 1 as your start date I would be ready to start interviewing the remodeling companies by the first part of January.
This is the way our process works:
One month to interview remodelers, make a decision and enter into a design agreement.
The design process for an addition is approximately two months.  This depends on the complexity of the project and your ability to make decisions.  When the design process is concluded we will present you with a construction contract.
Upon acceptance of the construction contract there is usually a two month wait.  This allows for permitting, material ordering,  proper scheduling, and other logistical matters.   
That totals 5 months.