With any building, size matters. The square footage surface area, followed by height dictates the cost. The two factors that greatly dictate higher costs are width and height. Length is purely additive. So, the narrower and the lower the building, the cheaper the cost, and vice versa.
Even after you order a building, you can always add more length later. But you cannot change the width or the height.
The best way to determine the surface area is to stake it out on the ground for width and length. Maybe place some of what will be stored in the building (cars, trucks, etc.) within the staked area. If it is a horse arena, consider how you will use the inside for Western or equestrian activities. This allows you to be sure you can open side doors and get in or out of the parked vehicle, or in the case of horses, leave room for turning at canter. You will be surprised at how much this helps you configure square footage which has an impact on cost.
For height, there are several factors to consider. First, do you want a partial or full mezzanine upper floor? Typically, you would allow 9 feet below, 1 foot for floor rafters and then 9 feet above, for a total of 19 feet side wall height. Second, overhead door size(s), particularly on the side walls, are a key issue for height. A steel building typically needs 3 feet clearance above an overhead door height. This is a simple issue for a single-story building but needs to be carefully considered for a 2-story building. You cannot have an overhead door that is 16 feet high and side walls that are 20 feet high AND a mezzanine 9 feet high unless you keep the overhead door outside the area of the mezzanine because they simply interfere with each other and won’t work. Lastly, overhead doors on the gabled end walls can be higher than the eave because of the added room formed because of the peak height.
Inside the building, do you want a crane? A hoist is an easy issue because it is self-supporting. However, an overhead crane is built into the steel structure and so requires reinforcements not normally present. This is also the case for outside second-story decks.
Occasionally, you may want the inside of a building for an insulated workshop, storage, or even living quarters and yet also want to keep some equipment or vehicles under cover outside it. This can be accomplished by placing an open-sided ‘lean-to’ down one (or both sides) which could extend out from the solid building’s sidewalls any number of feet. Or, you can add a closed-in, all-sided addition. Height for either lean-to or addition would start one foot below the eave.