I'll cut right to the chase here. The description for upgrading buildings is the same for every building I have seen so far. For most, the benefit is clear; a level 5 barracks equals level 5 troops.
For others though, say my siege workshop, leveling it to 5 and comparing a newly built trebuchet to one built from a level 1 workshop there is no visible difference. Is there a resource I am unaware of that lets me see the benefits of upgrading different buildings, or is the only thing that increases in cases like siege workshop the build time of the units?