Building on walls and ceilings

[KurioHonoo]

I have seen screen shots of people having reactors built on walls and ceilings and i just can not figure out how to do it, help?

[Fisherck]

This is a special thing allowed only in special missions, and is not included in the storyline. But it can be found in certain bonus missions like Odyssey and Cubic. ;)

[mthw2vc]

Where are these screenshots to which you refer? :P
There is no secret to it, it all depends on what map you are playing. Specifically, you can do it in bonus levels six through nine.

[KurioHonoo]

thanks guys!