Many of the shawl ministry websites discuss rectangular wraps as well as triangular shawls. I think a wrap would be appropriate for a man. This website recommends making it at least 26 inches wide and a minimum of 68 to 72 inches long.
I would suggest looking at men's scarf patterns, since they are designed to appeal to men, and casting on extra stitches to make it wider. Since you do not want to make a pretty, lightweight, lacy shawl, some of the ministry websites suggested using a bulky weight yarn for warmth and softness. Apparently, worsted weight yarn tends to be stiffer and rougher against the skin after it is worked. This can be a problem for the elderly or people undergoing some types of medical treatment.
I hope this helps.