You should start with the architect, as in almost all cases you're
going to need a set of plans with an architect's seal to get a building
permit. The architect is the guy who knows design so the addition
looks good, is functional, etc.
Neither. First, find out if it is allowed under your local zoning and or
building codes. Then talk to an architect. You may want to talk to
contractors to see if they are interested in doing the job as a time saver
for later though.
Not sure where you live, but you could contact a couple builder/remodelers
and have them give you some idea what it would cost.
I added a second floor to my home in Ohio 25 years ago. I started out
planning to have it done entirely by a contractor, but when their cost came
in well above what I could afford, I used the ideas they'd presented and
hired a guy to help with the heavy stuff and did all the finish, electric,
plumbing, etc. myself.
Of course I had all the necessary permits and all, so everything was done to
code (or better).
Scrape off half the paint, let the yard grow wild, and put on some ratty clothes.
Then get out the video camera, make a really pitiful tape of yourselves, and send
it to "Extreme Makeover: Home Edition". They'll build you a new house, free.
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