Hi, welcome to OpenStreetMap. Are you absolutely sure this building's walls are made of metal, because that's what building:material=metal means. You may have wanted to add roof:material=metal, which means roof is made of metal.
Also, if you are making changes within single contained area, then it's recommended to put multiple changes into single changeset - meaning you don't have to press yellow arrow every time it appears, only when you have finished editing or feel so. Everydoor will offer you to download data when it deems it necessary.
PS. Seems like you are conducting an organized edit, make sure to disclose that fact on your profile page.