@Micha That sounds like a fantastic idea! I was thinking just blocks that actually placed other blocks right in front or next to them, which would be much more tedious and limiting, but yours sounds so much better. A special editor sounds great, but so does a drone part that could replicate parts attached to it, maybe only those attached via a floppy tether or something?
I would love to see some parts that let your bot place things down in such a way that you could create smaller bots inside of your big one, so perhaps you could release 2 or 3 satellites that would just slowly pump out a swarm of little robots. I was thinking it would have to cost something, so that you cant just slap a few pieces on your bot and call it good. What about any fuel or power that it starts with is taken from the bot that made it, and it has a pretty steep cost to make each piece. You could make it so that the block placers run on either fuel or power depending on which you get.