Would a pre-existing plan account for the sun exposure of your land? Would it have a roof that makes sense for how much it rains or snows? Would getting sunlight in the bedroom also mean facing traffic? Would it take advantage of elevation for views or make sure to block a nearby neighbour? Would it deal well with moisture, or fires, or access roads? Would you build a porch where you can laze away late summer afternoons and feel everything's just right with the world, or a place to dry laundry where nobody goes?
If you really want to design your own house (a great idea), look up materials around A Pattern Language instead. Learn what makes a great house, then design a plan incorporating those ideas but customised towards your plot and your needs.