Some ideas on directions the mod can go. I would love to see it, but i won't push.
1: Bots place a 1hp version of the building and the building only becomes active when fully repaired, requiring resources over time to actually build things automatically. Makes it closer to Supreme Commander and how you construct things there. The cost of automatically building becomes apparent when constructing large things. Also allows other mods like Repair Towers to assist in constructing. It may require drastic changes to how repair packs work in order to not be too broken, however.
2: Multiple bots can "assist" a construction, reducing the total time to construct a structure with diminishing returns when more than one additional bot is assisting.
3: Bots require energy to construct structures (would automatically be done when #1 is implemented, because repairing mechanics. Also pairs nicely with #2.)
4: Structures placed automatically must be mined automatically. You can't pick up structures that you yourself haven't placed, but bots can deconstruct/reclaim manually placed structures.