Room objects in Revit do not have parameters on them to automatically report the length and width of a room. It would be fairly straightword to automatically calcualte these values if EVERY room ever designed was rectangular. But there are many other room shapes length and width are not so easily defined.
You can add shared parameters to a room object to be qable to add this infomration and have it report in a tag, but the sizes would have to be manually coordinated.
Jeff Hanson Sr. Subject Matter Expert Autodesk, Revit User Experience