most big guys, myself included, cannot use a typical shoulder holster. i'm not fat fat, but I am big. the question you have to ask yourself if whether you can swing your stubby little arm around your massive chest and draw that peashooter.
most shoulder rigs are a no-go for me. having said that, a benefit of being a big guy is that you can conceal a IWB or OWB holster pretty easily. I'm a huge fan (have I mentioned this?) of the Milt Sparks VMII.