You can hang a garage door yourself if you're comfortable with a torsion spring under full tension, a level line across a double-wide opening, and getting the track plumb on the first try. Most people who try this once don't try it twice. A torsion spring wound to the wrong turns count doesn't fail gently - it releases all at once, and it's put people in the hospital.
What you can reasonably do yourself: order the door, measure your own opening, and have the unit and hardware on site before we show up. What we'd rather you not do: set the springs, wire the opener's safety sensors, or trust a torque wrench you don't already own.