I agree that probably getting a garage building business to build your garage
for you is probably the way to go cost wise, time wise, and you will get just
as good a quality building if not better.  My dad is a contractor and we live
in NJ.  I would guestimate that just the materials alone for what you want to
do will run you close to $5000.  The floor will be a big expense.  People
think that they can do a building cheap but nowadays there really is no such
thing.  Also if you are going to do it, do it right is what my Dad always
says.  Skimping on building materials now will only create larger, more
expensive problems in the future.
One more thing.  Particle board or chip board is OK for interior walls but do
not use or let the builders use this junk on the outside or roof of your
garage.  When exposed to moisture this stuff just starts falling apart but
builders love to use it 'cause its cheaper than plywood.  Use plywood
sheathing.  You will thank me 20 years from now.
Ken Wilford
John 3:16