I do have one more question. Do you think I'll save money building a computer rather than buying one?
It depends on where you shop. I know some local stores around here used to sell Ubuntu desktops for about $200 but I guess they were not popular enough. Low end computers these days sell for around $300 unless you catch a sale for say $249 or something.
One problem with buying also is that you will be paying for a copy of Windows that you do not need, and it will be a copy that you cannot sell, what they call OEM. You could always install Ubuntu along side Windows, or even inside Windows using the WUBI installer.
You might find a deal on a used desktop, but you never know how long it will last. Whatever you get, just make sure it has at least 2gb ram. Ubuntu is no longer as lightweight as it used to be. Plus, any computer with integrated graphics is going to steal some of the ram for that.