Sloping tops: while most lockers have flat tops, some manufacturers offer the option of sloping tops to their range of lockers. The slope may be of either 30 degrees or 45 degrees to the horizontal, sloping towards the front, and the purpose of this is to make it impossible to store items on top of the lockers, or to make it harder for dust or other debris to accumulate there. This is an important factor in places like food-processing factories or restaurants where hygiene requirements must be met.
Laundry lockers are used in places like hospitals and food-processing workplaces where uniforms have to be collected, laundered, then returned to their owners. The locker cabinet contains a number of very narrow lockers, each of whose doors is keyed using a key held by the owner, so that they have access only to their own locker; but the entire array of doors is embedded in a much larger door covering the entire front of the cabinet. Opening this opens all the lockers simultaneously, and requires the use of a master key which is held by whoever collects items deposited in lockers, for laundering, then returned in the same way, after which they items are accessible to owners using their individual small doors.
For longer term storage, there are many self storage units around the metro area. Not cheap, but then neither is paying extra baggage fees and lugging around extra stuff not needed for another leg of your trip, as it sounds like Terry might be doing. For example, I found "Downtown Denver Self Storage" with units starting at $45 a month. http://www.downtowndenverstorage.com/
Tiers: may be specified as single-tier (full height), two-tier, three-tier, etc., meaning that the lockers are stacked on top of each other in layers two high, three high, etc. Tiers are commonly up to eight high; on occasion, even more tiers may be found, in the case of very small lockers for such purposes as storing laptop computers. The most common numbers of tiers found in lockers are, in order, one, two, and four; three-tier lockers are rather less common, and other numbers such as five, six, or eight even less common still - seven almost non-existent. Since locker cabinets are most commonly 6 feet (182.9 cm.) high (although there are exceptions), the height of individual lockers varies according to how many tiers are accommodated within the cabinet. The height of individual lockers is usually approximately 6 feet (182.9 cm.) divided by the number of tiers, so that two-tier lockers are about 3 feet (91.4 cm.) high, three-tier lockers 2 feet (61 cm.) high, four-tier lockers 1.5 feet (45.7 cm.) high, and so on. Standard features often vary according to the number of tiers: single-tier lockers usually include a shelf about a foot (roughly 30 cm.) from the top, and a hanging rail (sometimes with one or two hooks) immediately underneath that, at the top of the large compartment beneath the shelf; two- or three-tier lockers usually lack the shelf, but include the hanging rail; lockers with four or more tiers usually have none of these fittings, but consist of just the bare compartment.