Cage builders are like cabinet builders...they only start when the money is there or at least a deposit (depends on the size of the cage builder). Now, it could be a busy time for cage builders, hence why they ran out of material, or their supplier may be slow to ship etc. This can happen with any construction/building business. Its annoying yes, but not much you can do. You can complain to the business, they may throw in something extra (light fixture, gormets, etc whatever) to ensure you are a happy customer despite the delay. Some won't, it really depends on them. They may even offer a discount on your next cage purchase...definitely something you can ask for.
Another thing, having a large selection of pre made caged lying around means storage space is used up, space that could be used for materials etc. Again depends on the company's size and how much space they have to use up for 'display' cages. It also depends on what size/type/color cage you ordered. If it it isn't the most commonly requested design/color etc, having pre made cages of that kind, is really pointless, as it may never sell or be years of sitting there..and designs may change or colors no longer be available, or other modifications which may not make it compatible with later models.
Only thing you can do is express your frustration and disappointment to the cage manufacture. Only they can address your concerns and help alleviate them. If they value customer experience, they may give you something to reward your patience etc. But don't expect it will happen every time there is a problem.
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PHLdyPayne