But surely, given how big it is, such "component" building like in those pics is a little unrealistic? If it's 900km across I find it hard to believe traditional construction techniques really matter as regards a framework. Add to that the fact that it's being built in space, and I find it even less important. That's also one of my issues with the framework we see at the end of Episode 3, it looks like the DS I has a simple metal framework but at that scale those frames would be several kilometres thick. I don't think that's likely.

EDIT: Your additional idea about Star Destroyers or similar towing decks into place, I think the same point of scale applies. On such a massive structure, that's probably how it was done but you just wouldn't be able to see it.