For all of you guys with lacking room, I have a solution, not pretty but pretty affordable, atleast for my area.
I bought one, and shelf is a MUST for
parts. I only put 2 layers and it opened up all of my sheds that I basically couldn't even walk in before open up quite nicely, and the shelf is only one side and about 28ft long. The shelf isn't fully loaded either, just boxes of
parts labeled per machine and stashed. Light/big stuff up high, common stuff on the mid shelf, and heavy things like engines etc on the bottom/floor. I made the shelf about 24in deep if I recall correctly, plan is to make another shelf exactly the same on the other side, but right now I have some machines stuffed in there. The last like 6ft is my "overflow" stock for my business so it's not eating up all the space in my spare room in my house.
I have a second one coming this week, my logic was that would be more for whole machines. I haven't determined how I'm going to go about it, but I'm thinking a single layer shelf roughly 4ft high would be pretty ideal. Having a chain fall on a roller system would be really nice for getting the machines down but that can also be quite costly, so simple solution is a ramp at the end of the shelf and maybe a chain fall to pull the machine up the ramp if needed (there's metal loops at the top of the walls). Just think a line of machines around 30ft long double stacked plus some more basic storage on the other side (like 12in shelves I think there would be room for) with a walk way in the middle.
For my area delivered the "normal" price is $2350, since I'm buying more than one and such the guy knocked the first one down to $2250 and the second one he's giving to me for $2200. I'm half thinking about grabbing a 3rd one, I burn wood for my primary heat source and having a container full would be something like a 5 year supply. Clearly would have to dry the wood well before being stored, extra vents made, and probably some sort of floor setup to allow air under the pile. I was going to build some cheap wooden buildings for wood storage, and even if I got the walls free it would still cost more than the shipping container for the area, and it's a metal building that can be moved around somewhat easily with equipment, no tax worries, etc.
Of course I live in the country where the "ugly" shipping containers can be used. I suspect in the city it's a bit harder, but I've seen some people get away with 20ft ones on youtube.
I don't think the cost per area can be beat until you start looking at fairly large pole barns, then the open floor vs a narrow hallway layout becomes worth something too besides raw area. I plan to build a pole barn too, just haven't saved up the money for it yet. I do have the metal siding though already (steal of a deal $20 per 20ft sheet of very heavy stuff).
Everyone's situation is different, but if you can get shipping containers for a reasonable price, they are pretty hard to beat. A $75 lock secures it pretty well too from most basic attacks people would try, it's that or build a lock/box setup so a quality padlock can be used but not accessible to grind off quickly. I read one of the most common attacks is a long pipe with the end modified/welded to hook in the padlock area and twist till either the lock breaks or the metal tabs bend/breaks.
One problem to deal with is even during the day, far in the container is fairly dark so a flash light or lighting of some sort is pretty much needed. I plan to run a single circuit into mine for a mid row of lights and maybe a 2nd circuit for a power outlet (battery charger, small things like that). I have a building like 15ft away to run power from and was part of why I picked the location.