the ArcGIS.com map viewer is not able to measure area...yet. It's something we're planning on including in the future. However, you can do this with ArcGIS Explorer online using the measure tool.
I don't know. You might check out the samples in the API references. One site that I do know about is an application called Boston Solar. This app lets you click on a building to determine solar potential. I assume that behind the scenes, it must be doing some calculations. It's build with the ArcGIS API for Flex...
I am Durgaharish, I want to know is there any tool available for calculating roof area using community maps of arcgis. I am wondering how solar boston built that tool. Please help me in this matter.