I saw the ai often building or rebuilding turrets. So My question: Is it pissible to make the ai rebuilding things like the auto-defense-mainframe or the shield-generator? And if Yes, how?

Try adding to the object's odf.

this makes the object rebuilding, i know.
Bot i want a UNIT to repair it using a fusioncutter.

at this number it won't repair itself, but i noticed that any building that gets repaired by AI has this odf line, while the ones ignored by AI don't.

the autoturrets aren't repaired by bots and respawn because this line after 60 or 120 seconds (not sure with the number).
But I'll try this out.