A knockdown unit comprising a framework for holding one or more panels and one or more doors, having two outside vertical jambs; at least one vertical mullion; at least one horizontal frame member; at least one sill frame member; the vertical jambs, the at least one vertical mullion, the at least one sill frame member and the at least one horizontal frame member being connectable at a job site to form the knockdown unit, an upper end of each vertical jamb being connected to the at least one horizontal frame member, a lower end of one vertical jamb being connected to a sill frame member, a lower end of the at least one vertical mullion being connected to at least one sill frame member, an upper end of the at least one vertical mullion being connected to the at least one horizontal frame member.