Hi Alice, the vast majority of footprints here represent buildings, though most of the circular footprints actually represent vegetation i.e. bushes and trees, due to their colour. Zooming in and out tends to aid imagery interpretation.

The NW circular footprint looks like it should be square. 

It looks like you mapped the building footprints smaller than the roof, which I recommend when mapping buildings with pitched roofs to account for roof overhang and reduce the likelihood of data overlaps, however some of the footprints are otherwise not as accurate as the imagery allows them to be in for instance, orientation, aspect ratio and position. 

When mapping buildings, please trace the shape accurately. Accurate building footpritns aid population estimates and prevent issues like data overlaps. Zoom in so that you can see the outline of the building and mark the corners carefully. Exclude shadows and yards when tracing the footprint. Keep in mind that you are looking at the [roofs of buildings](https://wiki.openstreetmap.org/wiki/Key:roof:shape#Roof_shape), but mapping their footprints. Depending on how the scene is lit, pitched roofs may have light and dark sections that belong to one building. Generally pitched roofs overhang the walls of a building, so a footprint slightly smaller than the roof is accurate. You can scale selected features in ID with shift+(-/+), or JOSM with ctrl.+alt+Lclick & drag.  Take care to make contributions that others can build upon.

I hope this is informative. Happy mapping. Please keep this feedback in mind when contributing in future. Thank you for your contribution. If you want to experience the OSM community or to get timely feedback from other mappers; I recommend that you attend a mapathon. You can find events here https://osmcal.org/