Am I allowed to buy stocks on chol hamoed in a situation where I will only be able to make money if I buy it now and not after yom Tov?

If a man has to choose between building his own sukkah and building his father’s, whose sukkah takes precedence? This is when his father is not strong enough to build one of his own and has no one else to help, and the son only has time and/or energy to build one, and the father and son do not live close enough to be able to share a sukkah during Yom Tov.