Can you tell me how high are my chances of developing chickenpox from someone with shingles?

Rare but possible. The shingles patient can only spread the germ through contact with the debris, not through saliva or a cough as would be the case with chickenpox.Also, at a listed age of 50, your chance of never having Cpx as a kid are less than 4%, even if you don't remember it. A simple blood test could prove you once had Cpx and are immune.