Under a contract whereby the parties agreed to put in cement sidewalks, build stone pillars, and write all advertiseemnts, in consideration of their appointmemt as exclusive agents to sell lands, "all of the above to be paid for by" such parties, they to receive one-half the net profits, the expense of putting in cement walks, etc., must be paid by such parties, and they are not entitled to have the same paid out of the proceeds of sales. Id.