Height of the garage door is going to depend on what you got up on the hardtop. I had to build my garage with a 13' 6" clearance due to a radar antenna riser that was tall. I subsequently had the riser lowered, and my boat now stands somewhere around 12' tall on the trailer (could measure it if need be). Don't forget, if you build your garage for a 12' boat, the door opening will have to be higher than that depending on door clearance in its raised position. Also, the walls will have to be high enough for the door tracks to mount above the height of the door to the bottom of the tresses, for the springs to mount to the header above the door opening, and for the door to make the turn above the track height. I made a slight miscalculation on mine and had to stand on a ladder 14' above the ground cutting 1" off the bottom of one of my tresses and a half inch off another with a circular saw. That sucked. For door clearances you should contact the door maker, and it also depends on the track and lift mechanism you wish to employ.
P.S. Of course, if you use doors that open outward, that greatly simplifies the measurement aspect. :wink:
