Buying off-plan means committing to a property before it's built. In return, prices are usually lower than for a finished villa.
With a 30/70 plan, you pay 30% of your share as a deposit to reserve it. The remaining 70% is paid in stages as construction milestones are reached.
An example
For a 10% share priced at US$26,900, the deposit is US$8,070. The balance of US$18,830 is spread across the build, rather than paid all at once.
Staged payments tie your money to visible progress on site, rather than paying for a property that is not yet built.