I use the grid on the scene. The Building A (first image) setup is to be expected. But when I uploaded Building B, the orientation didn't match. Do I have to set it up in Revit ? or can I do it programatically.
Every model you load into the viewer is coming with its own metadata such as:
By default the viewer honors all these settings which means that, for example, if you load a Revit model that is defined in feet (and uses the Z-axis as the "up" direction), and then an Inventor model that is defined in meters (and uses the Y-axis as the "up" direction), the two models will have different scale and orientation.
To work around this issue, when loading (aggregating) multiple models in Forge Viewer, you can override any unit scaling, offset, or general 4x4 transformation that is applied to each model. For more details, look at https://forge.autodesk.com/blog/multi-model-refresher.