I have a 10' x 10' door in my garage and if it were not for the power door operator, I wouldn't consider using it very often. If you are considering a 16' x 12' door, you will definitely need a 1 HP commercial door operator. The quick way to determine door heights is to remember that all commercially available doors are made up of 21" and 19" sections. Just figure that 7' = 4 - 21" sections. 8' = 5 - 19" sections. 10' = 5 - 21" sections and 1 - 19" section. 12' = 3 - 19" sections & 3 - 21" sections. Doors may be ordered in increments of 8', 9', 10', 12', 14', 16' as standard sizes. Today, most doors are installed with torsion bar suspension as opposed to the old fashioned draw springs. The most important thing is to make sure that the door opening has the proper mounting framing to accommodate the door hardware. Many door installers will comment that they have to "repair" or add lumber to the framing so their mounting hardware will be properly supported. Also make sure that your electrician supplies a live box for the door operator. Personally, I wouldn't go larger than 12' x 12'. Shop around for the best door that you can find, because the sweetness of price can often lead to problems later on. Many doors today have insulation in them and are of good quality, but I have seen some doors that are so poorly constructed that they have to be replaced in a few years. You might be better off if you contract with the door company to do the installation rather than having your general contractor do the installation. Remember service after the sale is important.
One last thought that just came to me... If the floor is to be installed after the building is competed, then you will need to adjust for the floor thickness when planning the door opening. I have seen where contractors don't take this into consideration when erecting these type of buildings because they figure that it will always have a dirt floor. Considering the size of the proposed building, I would suggest that you go with a 5" or 6" thick floor... the small extra cost is well worth the investment. See other threads about pouring concrete floors and insulation / poly underneath them.. My last floor was poured 6" thick, with high strength (4000# mix) concrete with chopped fiber glass and reinforced with steel mesh throughout and 1/2" re-rod reinforcing at the door openings over poly. Solid as a rock and dry as a bone....