Eliminate the lawn inside the first section and change it with an appropriate material for a flooring.
That's what the excellent thing about minecraft is: even the most ordinary or dull parts of the game can result in something remarkable.

When you're through with that, which will take rather a long time, tunnel to where completion of your glass work of art hits the earth, and get to digging.
Well, it's not simply an easy video game of virtual Legos.