One of the worst potential downsides to a material building supplier is the depreciation of materials that are left within a warehouse over time. On top of the value depreciation, there is also the worry of having the materials actual quality diminish over time too, especially if the materials are not packaged in a professional way.
The first main issue when it comes to the aspect of material quality lowering is worrying about potential hazards that are uncontrollable. At any point, there could be a rainstorm or enough rainfall over a significant period that some water or humidity will lock within the building itself. This could cause dripping within the building and onto materials itself. This will mean you have to worry about anything from rusting with nails and large metals to overall rot or woodworm from wooden planks or other important materials.
Another aspect you must worry about is the ever-changing economy for materials in the first place. There are so many different dependencies when it gets to the actual value for your materials. Especially depending on the type of wood that is supplied. And with the wood, there will be a significant increase or decrease of how much that wood is worth. Oak, maple and every other type of wood all have difference prices, and the more a local economy is farmed for their materials, the more these couple be worth.
On the flip side, the more a certain type of product is supplied within an area, the more the value of these items can depreciate. Either way, there will be a significant increase in the costs of holding these supplies over a significant period. Few suppliers would purchase materials in bulk, especially if they cannot find builders or construction companies that need these materials before they are purchased.