Bigger is better, I guarantee it. Size matters.
In 2008 I built a 50 by 90 steel building, 4,500 square feet, clear span.
Figured I wasn't going to do this again, might as well do it right the first time and be done with it.
Forgot all about Murphy's Third Corollary - stuff expands to fill the space allotted to it.
Dang thing is FULL . . . some of the stuff isn't even ours, a friend says hey I need a place to store X for a few weeks (right), and it is hard to turn friends down, they reciprocate in other ways. Same for extended family - they are a bit easier to decline, gee, it isn't heated or cooled, and there are sometimes mice and bugs, so they look for alternate storage accommodations.
There is also furniture in it for an addition we are building, and materials for that addition. I work on our vehicles in it as well. Workbenches, tools, lights, power, music and a small fridge - Dear Bride always knows where to find me, and I'm OK+ with that.
Very glad I did it, it has been endlessly useful. It also makes a good place to park our cars during a hurricane, it is rated at 160 mph and we are not close to the coast. Hurricane shutters in there, too, when not needed (which is most of the time).
It also generates income. I work with a small overseas company which sells on Amazon, all the returns come here. (Amazon won't ship them back to him, instead they'll just discard them.) He has about six pallets in there, and I get some nice pocket money every month (yes, I declare it ;-)
Don't be afraid to build it BIG and build it WELL - you won't regret it.
Best Regards,
Mike/Florida