Flashing girth widths vary greatly between 8mm to 1200mm. Any flashing that needs to have a girth larger than 1200mm would require one or more seams.
You should also take into consideration how much roof overhang is allowed — for example, corrugated metal sheeting has a 100mm maximum overhang when unstiffened (up to 300mm when stiffened).
Mid wall flashing is typically spaced 4 to 6 metres apart for horizontal metal sheeting. In general, you will have metal sheeting laid directly adjacent to the mid wall; creating a continuous sheeting arrangement that is sealed with flashings. A simple sheet overlap is not often suitable, but may be with certain metal sheeting products.
Internal corners of vertical sheeting can be sealed with either a simple trim or a three dimensional mould.
External corners should use a three-dimensional mould to seal, particularly with horizontal wall sheeting.
When sealing the flooring of a wall with flashing, make sure there is proper drainage and install it in a way that avoids debris build up.
When installing flashing on a roof, you need an adequate drainage path at the front and sides to prevent ponding. If your roof has closely pitched ribs (most corrugated steel), a soaker arrangement is needed.