Moving platforms?

The best way to create a platform that moves along a set path would be to use func_tracktrain. However, we'll quickly run into a couple problems. Firstly, engineers can't build on top of func_tracktrain, at all. We can avoid this by parenting another entity that engineers can build on top of, such as func_brush, to the train. The second problem is that when placed on an entity, buildings won't actually stay attached to the platform and will remain in place long after the entity has left, leaving us with a floating engineer building. We can use a trigger_multiple entity to detect when an engineer builds on the platform and parent their building to the platform. You can see all of this in the example VMF/BSP attached to this post.

(Some issues to note: Dispensers don't seem to update their trigger area when parented, so the area of effect of a dispenser will remain where the dispenser was built while the dispenser's physical model floats away. Teleporters function as expected, but some of the particle effects look a bit off while it is moving and the arrow on the teleporter entrance does not update to continuously point at the exit.)