Ortlieb Profi Bag
If you're looking for a waterproof briefcase style bag but don't like the hard case option, this will do the job. Features a roll-top dry bag closure and seam-sealed PVC coated 500D Cordura. This bag is truly waterproof. Ideal for foul weather field work or wet commutes. Large enough to be used as a wet weather shell over other laptop cases. Features include: Plastic stiffeners on the bottom and all four sides, removable padded shoulder strap, and internal organizer pockets. Lifetime guarantee. Dimensions: 15*11*6