A friend asked me to advice which one he should go for with a Ksh 1 million budget. He is a freelancer so he has a lot of free time. Below are his two ideas:
1) Buy a plot worth Ksh 1 million and figure out how to build later.
2) Buy a car (Probox or any other bachelor's car) at Ksh 350,000 and invest Ksh 650,000 in a brick and mortar business. He figures that he will need the car to efficiently multitask between freelancing and running errands for the business.
What should I tell him?

Let him put his money where he will get the highest profit.

You need to provide more information...
especially on the Brick and Mortar business. That kind of business might not be viable with a Million or less as capital investment. What area is the business set up? What the target income? Is the Mil a loan?
The Probox is obviously Salvage and will depreciate in value every month.
The Plot! where is it? 3rd or 1/4?
Leasehold or freehold. Water, electricity and tarmac road access? Tell me more.