Flashings should always go on before building wrap. It is also important to note that Z flashing is installed before counter flashing.  

Step Flashing (Z Flashing): Step flashing, also known as Z flashing, is a type of flashing that is typically installed first. It consists of individual metal flashing pieces shaped like the letter "Z" or "L." Each piece is placed between the roofing material (e.g., shingles) and a vertical surface (e.g., a wall or chimney). Step flashing is designed to create a waterproof barrier and direct water away from the roof-wall intersection.

Counter Flashing: Counter flashing, on the other hand, is a separate piece of flashing that is custom-fitted and installed over the top of step flashing. Its purpose is to cover and protect the exposed top edge of the step flashing and provide an extra layer of waterproofing. Counter flashing is typically sealed in place and provides a clean and finished appearance. It also acts as a barrier against moisture, preventing water from getting behind the step flashing.