I’m approved for an sba loan but is not enough to purchase the land and build a 6,000 square feet building. Should I wait a couple of years on the project or should I apply to purchase the land? 

If you just own the land you have no income coming in usually off the land until you start to improve it. Have you approached the owner for owner finance loan at possibly better rates and terms than what the SBA lender offers?

Maybe I should just wait to earn more money for the down payment