If you look at the other buildschool plots you will find some finished examples as a kind of showcase like you are doing atm. There is no real "protocol", it depends a bit on what you actually want to teach. It should be something that can be done as a group event in one evening. In your case I suggest you narrow it down to spaceships atm and have those examples you already built, plus maybe 2-3 more general builds. I could imagine a rocket for example, maybe like a spaceshuttle or something very alien. Who says there cannot be green, organic spaceships?
There is alot to build around the space theme, as it's totally different from what the default minecraft world has to offer. You'd need housings, vehicles, plants and terraforming, interiors and general technical decorations. Thats why I say focus on ships to start with, or it will be too much.
Once you've built up the examples I suggest displaying parts of it, like engine shapes, weapons, which palettes to use, detailing tricks. That way, folks don't get so easily overwhelmed by looking at the whole thing. Makes it easier to understand what you did and easier to copy.
The last bit then would be for everyone to build their own spaceship using what they have learned with you and maybe an assistant going around and giving pointers.
