It may be - but it's a gamble. You are giving them money for something that doesn't exist, and when it is built the value may be less, for many reasons.
Some people make a lot of money buying off plan and selling for a massive profit. Other people have lost a lot of money.
You need to research the market. A good pointer is to look at the number of established properties for sale in the immediate area. Are they selling well, or is there a glut? Are there plans to build lots of new properties?
Research is the key.