There's nothing to suggest Weyland-Yutani built the Nostromo. In fact, Ash, the one mission-critical piece of hardware which was installed on the ship before it travelled derelict-wards, was built by Hyperdyne Systems, not Weyland-Yutani.
To this day, we haven't had any indication as to whether the Bishop synthetics were made by Weyland-Yutani, either. Just assumptions. Unless you feel the AVP films are definitely canonical, of course (some do, some don't).
Same goes for the colony. Burke points out WY build the atmosphere processors, but says nothing about the rest of the place.