Google Earth Pro added "Measure in 3D!" to the Advanced Measurement Tool Suite.
"In a continued effort to mirror the real world, allowing you to lift measurements off the ground and extend them in to the 3D realm seemed a natural next step. 3D Measurements can be used by engineers to plan wind farms, real estate firms to determine skyline views for new high rise buildings, construction companies to measure the materials needed for a retrofitting, architects to calculate the space between buildings, and more," stated Google.
To measure buildings and distances between buildings, just turn on 3D Buildings layer and click the Ruler Tool icon in the toolbar. If you're running Earth Pro, you'll notice two new tabs for measuring in 3D: 3D Path and 3D Polygon.