Thiago
The main difference of buying off-the-plan properties from established homes is that you only put a deposit now normally 10%) and have to come up with the remaining amount only at settlement in a few years when the property is completed. The seller will be holding your deposit in a trust account and change of ownership will not happen until settlement.
For those who will require a bank loan, you must ensure your are "loan serviceable" closer to settlement and not necessary now when you are purchasing. In some cases this is beneficial as you can secure a home today and have a few years to get prepared to take on a mortgage.