I hope you enjoy the process it can be very exciting and rewarding to see the home of your dreams being built.
I would think if you are going with a custom builder you would want to start now on the lot research with an agent. Right now land prices are great but will rise with increased building activity.
If you are going with a bigger builder like Drees, Ryan, etc. there are limits on how long you can hold a lot before starting construction. In that case you might start researching builders and neighborhoods later this summer with a goal to break ground by January 2014.
It is an exciting undertaking but a good realtor can be a blessing.
Check with a couple of the custom builders, like Potter hill, Freedon Homes, Schumacher Homes, TK Builders, Anderson Homes, etc., to name just a few. These companies are set up to build on your lot.
But do contact a Realtor. That way you willl have someone to guide you through the process, and help you find the special incentive "deals" when available. Note; Builders do not charge you more when you use a Realtor to assist you. They build our cost into their marketing expense.
If you have any further questions, you can contact me.
Call me if you want to go look at some new construction; 513 225 0045