I don't know about your construction technique. What does come to mind
is, first, do you need permission
of HOA to expand the basement and/or deck? If you do, indeed, expand
the basement and put the deck over
it, I would surely have some hinged panels to alloc access to the
basement roof (sloped roof, of course). And
if you are planning to stay there a long time, why on earth do you want
to be able to dismantle the deck and
take it with you?