Your getting good advice on height and size.
I want to add that if you are going to build one spend the extra money and get a good one. At my house there is a Morton Building and it has been there since 1983 and is holding up very well. I have seen people put up "no name brand" buildings and they are just not built as well. For one thing if you are going to be adding any sliding doors the cheap building have doors that are built so flimsy that on a windy day you can not get them open because they flex so much. The quality and gauge of the steel on cheaper building can be bad too. I'm not saying it has to be a Morton building, just don't put up a cheap one.
Also, consider adding a side door. Or, if you have the space a door on the other end so that you can move things though. If you only have a door on one end you have built a cave. Then anything that gets stuck in the back on the shed (even a small item ) can not be removed unless you pull out everything that is on front of it. Sometimes it's nice to be able to slide open a side door to access smaller things you have stuck in the back of the shed. A lawnmower, or small trailer, for example.