flat tire

Last summer I learnt not only how to change a roof for old rural house, also I excelled as a tire guy. During last summer I changed tires for our old junk car at least six times.  To this day I still don't know why we got so many flat tires (most probably, because I bought cheap used tires at local tire workshop). Anyhow, it was the next morning after we added first metal roof plates a top of our house, when I noticed a flat tire has happened again (without any reason).  I was already equipped…