Ortlieb measures 13 inches from hook to bottom. rolling just once will give you 16 inches of height,
, but you may want to roll them more water resistant .. the strap down lid may give you more height
still width limited to 10''..
have you considered the travel biker , its a rack top briefcase like bag with their waterproof zipper around it.
Snaps on and off with a QR mount. or consider

'Office' line .. some Bags made to haul computers on bikes :
http://www.ortlieb.com/index_white.p...e=p-search.php