Anthony,

Yes, that is probably a very good idea. I do not know why I did
think about. I guess because the way the garage is right now and
because I have not seen in the hardware store anything longer that 16
feet. I will check tomorrow in a lumber store for 21 feet joist.

However, I do not understand how the floor joist will server as
collar ties because I planning to have 6 feet walls on the side for the
second floor.

Thanks a lot.

Claudio