What are the advantages and disadvantages of having drive-up climate space with exterior doors?

I would say the main advantage to outside access to climate-controlled units is convenience to the customer. Most customers want to be able to drive right up to their unit and not have to push thair stuff down long hallways on a cart. Your biggest disadvantage will be the energy costs. It is much harder to insulate the space at the top of a roll-up door and you have no control over how long the customer keeps the door open and heats (or cools) the outside. Most of the site plans I have done put standard storage on the outside, an insulated wall, and the climate-controlled units on the inside. Then the standard storage acts like an extra layer of insulation. That's one reason why you will see very few bare walls inside a climate-controlled facility - with the possible exception of units facing windows for the advertising value.