Q354: What are some good (Su) abilities on Monsters which I could acquire through Shapechange in order to build things? Basically all I can think of myself is a Beholder to disintegrate away obstacles and larger forms for logistical purposes. Are there any monsters with supernatural fabrication, wall spells, or other useful construction skills?
A354:
Delvers (core) get (Ex) Stone Shape. Obvious but there you go.
Earth Whispers (RoS) get Control Earth Creatures, which is rebuking for creatures with the earth subtype, a lot of which in turn have the (Sp) abilities you want. Kind of roundabout, but hey.
Earth weirds (MM2) may be able to summon a gang of earth elementals as a supernatural ability depending on whether your DM decides to let you sprout an Elemental Pool when you turn into one - the pool is a (Su) ability but you may get slapped for this. Also of interest is that Weirds get a big pile of divinations as at-will free-action (Su) abilities, which isn't terribly relevant to your question but is kind of interesting and I didn't remember it until I started digging around on your question.
That's all I found looking through creatures with the earth subtype. Lots of (Sp) versions of what you want, not really direct (Su) I could find.