Sounds like you are going to put up a wood framed building with steel siding. There is nothing wrong with that except it is not really a metal building. I have built several steel framed, steel sided buildings and there are a few suggestions I would make. Have the trusses designed for whatever spacing you choose. Trusses designed to be placed on four foot centers will probably be a little more expensive than those designed to be placed on two foot centers. Then decide.
The size of the windows doesn't make much difference. The placement will be more of an issue because it will affect the use of wall space and air flow inside the building. The twelve foot wall height is adequate for most uses but it might not be high enough for a lift. If you have plans to work on any kind of heavy equipment you might consider going 16' high at least. In my opinion, the doors you have planned are too small. I would go at least 36" wide on the walk through doors and 12' wide on the garage doors. Roll up doors would work very well, but if you go wider than 12 feet they have to be built to withstand windload and start getting very expensive. Roll up metal doors 12' by 12' would be just right unless you plan to work on combines or swathers.
Rainshot gave you good advice. I am just expanding on what he said.,
Last edited by 45_100; 01/18/21.
