In order to have a fixed building placement you must first have a fixed footprint. This will work just like the vespene geyser and the ability to build the refinery specifically at that location. Its very easy to do but its important to have a validator in order for this to work. Check out this thread and study the picture at the bottom of the thread, That all that is needed to do to get this working. The picture shows what is required for the refinery to be built on the vespene geyser.
Weirdly enough though i've been successful already trying out some things on my own, and the final result does not need vespene behaviors etc. in any way.. So, since your thread is a year old by now, maybe it's outdated and somewhat fixed?
All i did was the following:
- Duplicate a building (sensor tower in my case since i needed a 1x1 footprint, the object that will be the place where you can build seems to need structure properties though (dunno which exactly))
- Set the duplicated sensor tower as the "object" you want the other building to be built on (here i took the original sensor tower, set the duplicated in it's 'built on' setting and done)
Its great to hear that your getting it to work! :) however, I never said you should use the vespene behavior to get this working, I just use the vespene geyser as a example, The picture just shows what is required for the refinery to be built on the vespene geyser. What was important for me was to have a validator on what your building in the object values if you want units like the SCV to build on certain structures at specific locations of the map.