expand a appartement?

is it possible to buy a appartement with only 1 room, and then later if i want,
expand it to have a balcony and maybe a extra room?

if this is possible..
how much would it cost me?

No it's not.

There are different apartment sizes though...

as perivously said not currently possible but something like this was on an old and mostly uncompleted road list

How sweet would if be if you could purchase two aparments next to one another and virtually knock out the wall between them in order to expand?

That would be sweet and I would pay the monthly maint on both in an instant to be able to do that and have a place twice as big.