Quad Band GSM PCB Antenna
I hope you realize that antenna design is a very large and complex subject ! It might look like just a strip of conductive material (and actually it is :) ) but there's more to it than that. If you want the best performance (and you do since you want the product to operate in a basement) then you will need a "proper" antenna. If your antenna is not "proper" you might suffer from:


less transmission power because of impedance mismatch
less receiver sensitivity because of impedance mismatch
the antenna's radiation pattern might not be what you want


I don't think that just making a certain shape using the copper on a standard PCB will result in a very good antenna. For sure it will work but it will not be optimal. I would advise you to look into ready-made antennas that can be mounted on a PCB, here's an example. Note how it has a complexly shaped conductive area ! Also look at the datasheet, all information is there and it is guaranteed by the manufacturer. You cannot get that when you just make "some antenna" on your PCB by yourself (unless you are an antenna expert of course).