Check out this 23 July 2014 article from Tablet Magazine describing what the Palestinian people could have built, instead of smuggling / terror tunnels leading into Israel. At this point the IDF had, as the quote says, only located 18 tunnels.
"Israeli troops entering Gaza last week have so far uncovered 18 tunnels used by Hamas to send armed terrorists into Israel and built using an estimated 800,000 tons of concrete.
What else might that much concrete build? Erecting Dubai’s Burj Khalifa, the world’s tallest tower, required 110,000 tons of concrete. Hamas, then, could've treated itself to seven such monstrosities and still had a few tens of thousands of tons to spare.
If it wanted to build kindergartens equipped with bomb shelters, like Israel has built for the besieged citizens of Sderot, for example—after all, noted military strategists like Jon Stewart have spent last week proclaiming that Gaza’s citizens had nowhere to hide from Israel’s artillery—Hamas could have used its leftovers to whip up about two that were each as big as Giants Stadium. And that’s just 18 tunnels.
Egypt, on its end, recently claimed to have destroyed an additional 1,370. That’s a lot of concrete."Source: Concrete Facts About Hamas, Tablet Magazine