>>6
No, you would have to lift materials out of a gravity well in order to achieve free-space construction, unless you used asteroids mass-driven into Cislunar space to the construction site.
Hence, you may as well just dig into the moon to construct it.
The problem would remain of how to steer such a mass in order to aim the Ultimate Weapon, however. The moon masses about 7x10
22 kilograms ... that's 70 billion trillion kg, or nearly 100 million gigatons. Maybe we could slowly spin up some hypergyroscopes (each weighing a gigaton) within the moon, and alter their spin accordingly to point the moon's Weapon.