Hello and welcome to OSM!

Two little remarks:

- check the different values for building (https://wiki.openstreetmap.org/wiki/Key:building) as these look like  =detached

- after drawing the outline, select it and press 'q' to make it rectangular

If you have any questions (which you will have ;-)) don't hesitate to checkout the OSM forum, which you can use via your OSM account.

Some more info about how we do things is gathered in this article:

- https://wiki.openstreetmap.org/wiki/Good_practice

Have a good one!