At this point, the buyer becomes the owner.In fact, when the seller is a non-resident this liability actually moves to the buyer.
Various taxes will need to be paid, and the tax situation depends on residential status.Again, legal advice will be useful.Purchasing off plan will require all licenses and certificates to be issued, and that the property is debt free and bank guarantees are in place to protect the deposit in case the development is not completed.
When budgeting, be sure to allow for community fees, such as for the upkeep of the pool and gardens if applicable.