Everything. As you buy ammo, you'd be forced out of necessity to find ways to conveniently store it within the confines of your own home.
There's no other practical way to determine how to store your ammo because as the size of your inventory increases old means of storage are quickly rendered inadequate, thus forcing you to make changes on the fly. So unless you have an excess of space within your home which is viable for ammo storage, you're bound to encounter issues in regards to storage which are entirely unique to your specific living situation.
In other words, if you buy ammo at a steady pace during times of relative peace/prosperity, then ammo storage would most likely never become a substantial issue because you now would be storing it as needed up until the point that you either have as much as you foresee yourself needing or completely run out of viable storage space, whichever comes first.
The TC's question cannot be answered in any meaningful or effective way unless he were to divulge detailed information regarding the amount/volume of ammo which requires storage, where he plans to store it including the precise dimensions of the storage space in question, and the available amount of funds he has to devote towards the procurement of storage containers for the ammo.
Otherwise, folks can only make blind guesses, resulting in relpies which will more than likely prove unhelpful or otherwise inadequate for his needs, complete with folks defaulting towards suggestions which reflect their own unique methods of storage which have been tailored to the amount of ammo they possess, the available space in their home, and the funds which they have available to procure storage containers, thus resulting in responses which are all over the map with absolutely no focus whatsoever, most likely leaving the TC with by and large unhelpful information which may at the very best give him a few ideas, but he'll still end up having to do most of the work himself in a hurry, likely coming up with less than satisfactory results.