Setting just that edge won't help as the mesh may skew depending on the order you mesh in: you may need to set all the sizes. The warning just means you're not recording the mesh process so can't re-run it: look for selective meshing in Help.
In the interests of getting some results I'd suggest inflation on the building & ground and tet the volume. Maybe put a volume around the building & it's wake to retain a finer mesh. Then talk to your supervisor and see he they can talk to support or send you on training: as ANSYS staff I'm very limited in how much help I can give on a public forum.