Obviously, it's being made of something totally kewl, dude! since that appears to have been the primary consideration, how kewl it looks. This is what happens when you start playing games with these kinds of longstanding assumptions, like the bulk of work on the Enterprise's construction being done in orbit. Ya tend to ignore the reasons why that assumption was made in the first place, like maybe it makes a helluva lot more sense to build a ship of that size in orbit. Never mind that nothing in canon spells out the process explicitly, the logical problems alone should be enough to chuck this notion of building it on the ground out the nearest airlock.