It all begins with the foundation. The whole build starts with this step and it is an important step. The key goal of every addition is to not have it look like an addition and be part of the original home design. 

Layout, excavating, choosing the right foundation contractor is critical for a DIY home addition. Also important is the tie with the existing landscape. What to do with the dirt  that is excavating? Haul it away? What about items under the ground? Pipes, electrical and cable. Save your family some efforts and be diligent concerning the entry points of utilities. This should have been discussed with your architect. Relocating them is an added expense.