Get your door and framing material. If you are not a carpenter, this is a great time to invite a carpenter friend over to give you a hand. When you've built the foundation to the bottom of the door opening, set up the door frame, attach it to the foundation, level it, and brace it well. Putting the door frame up as you build the foundation and before you start cobbing saves you future headaches. You'll be assured that the frame for the door will fit well against the foundation and the cob. Carefully build the foundation to the frame. You can fill in any gaps between the frame and the foundation with cob later. Add the keying system to the frame so that it will be attached to the cob as you build. (See page 111 for details about keying systems.)
If you are doing a poured foundation, bury bolts into the concrete to attach the door frame to.
There will be a potential rot spot where the wood door frame comes closest to touching the ground. Handle with care.
Raise the frame off the ground with a flat stone or sturdy brick. Make sure that whatever you use will not get in the way when the door swings open.
If you want to add another room in the future, extend the foundation for the addition while you are building the present foundation. (You don't have to build it all, just the first 1-2 feet.) This will ensure a strong connection between the two stages of the foundation.
Make a second threshold and door frame leading into the future addition.
If you haven't found a door yet, make the opening to fit a common sized door. Leave the door open for easier access while building. Then insulate and board up the opening, or have two future addition outside doors until you add on. (See page 100 for more on future additions.)