Hello, 

After tracing and tagging features which are likely square or round, please remember to square their corners `q`, or circularise them `o`, because it is almost impossible and time consuming to draw shapes so percisely manually. Buildings with metal or pitched roofs tend to have square corners; round buildings are identifiable by the distinctive cresent shaped shadow they cast.

Unless the building is clearly a different shape then it's best to assume that it should be rounded or its corners should be squared. In the ID Editor, you can `right click` for access to editing functions. 

Since roofs tend to overhang walls trace the initial shape slightly smaller to allow a buffer for any change in size which may occur. In JOSM use the [buildingstools plugin](https://wiki.openstreetmap.org/wiki/JOSM/Plugins/BuildingsTools). In ID you must draw the shape accurately enough if you want every corner to be squared. This [video about squaring features in ID](https://youtu.be/Xs5wX592E1o) has more information and a demo.