Thats actually the perfect way to start a garbage map.
You'd benefit much more from building your map inside out, e.g start with the structure where the control point is located, then build the area around it, then go on with the next areas and so on, all while testing the map very regularly to check if it "feels" right.
You CAN of course do it however you like, but you won't learn much besides the basics from making box maps.