If a place is colonnaded, it has a colonnade: a row of tall stone posts that hold up a roof or a row of arches. This is a describing word, not the name of the row itself. The row is a colonnade; the porch, courtyard, or building that has one is colonnaded. People use it in architecture and in guidebooks — a colonnaded porch, a colonnaded square. It tells you how the building looks: columns are part of the face it shows the street. You would not use it for a house with two ordinary pillars by the door; it suggests a real row of columns, usually on a grand building.