I know, I know, kinda tough to answer. Really I am just wondering if we have any pros here that I can talk to about it. Bump me to another forum if required.
First, get an architect to draw up the plans and get the proper city or county approvals. Then get a qualified builder to do the work. You can do it yourself if you follow the plans.
Oh yes, if you do the building yourself, you must get inspections by a city or county official for plumbing and electric wiring and periodic inspections as the building progresses.
#1-What is it that you are trying to build? Doghouse, deck, 3 story suite with sunporch and heated veranda?
#2-What are the regulations in your municipality? Some want permits and plans for sheds, others want permits for average work, some don’t really care.
I’ve held permits and licenses in several states as a contractor, so I’ll do my best to help, but tell me more. Inquiring minds want to know. 
There are lots of local laws to be considered, but there are basic steps wherever you live.
First, make sure you actually have the room to build such an addition. Your lot may include easements (for utility companies usually) that will prevent you from building over certain areas. Also, consider the height of the structure if it will be taller than your home. There may be limitations to height in your area.
Once you are certain you have the room to build, horizontally and vertically, determine whether the structure will be attached to your house or not. The laws for attached and detached structures are usually different, and some attached structures must have a firewall between it and the primary structure.
Then you get the architectural plans, have them approved, hire your contractors, get your building permits, insurances, etc., and go to work.
Finally, have the work inspected and the final certificate of occupancy issued.
Thanks for all the input so far! More details:
We have a covered porch running the width of our house in back. Rather than just screen it in, I want to actually wall it in and divide the approx 40’ x 8’ area into smaller rooms. So, I won’t have to build roof, which is good, as I think that may be beyond my abilities at this point. I have practically no experience in building trades, btw, but I do believe I can do anything if I just research, ask questions, research, plan, plan, plan. I would probably contract out the plumbing, electricity, hvac, but may attempt one or two of those myself.
Checking with my city on footings, etc, seems to be my next step?