Fallout 4 Vault-Tec Workshop Size
Thanks to the game's recent release, we know that the Vault-Tec Workshop DLC is a fairly sizable add-on, larger than we thought it would be.
The Vault-Tec Workshop is over 700MB for the Xbox One and a little smaller for the PlayStation 4. This makes it larger than the Contraptions Workshop DLC but much smaller than the Automatron and Far Harbor DLCs.
If you don't have the space, it would obviously be wise to do a little cleanup on your system's hard drive right now.
If you're more worried about download speeds, try plugging your ethernet cable directly into your console to speed things up.