There is a wide variety of materials available for architectural model making, depending on your purpose, available time, and level of expertise. Foam is the primary and most commonly used base material for architecture models.
White foam boards are available in multiple thicknesses, most commonly 3mm and 5mm, and are solid boards that can be used as a base for models made from foam and other lightweight materials. They can also be used to construct walls, with the thickness chosen based on the scale. If the interior wall is not visible, the consistency does not matter.
Cork sheets are textured brownish sheets that are less thick and more flexible than foam boards. They are easier to handle and cut, but they can break easily.
Foam sheets are flexible and come in colors and small thicknesses, making them easy to cut with scissors.
Wood, especially Balsa wood, can be cut easily and painted, making it a suitable material for modeling. Wooden boards can also be used as a base for heavier models, and Balsa strips can be used for structures with wooden skeletons or to show trusses.
If your model is more conceptual or form-oriented, you can opt for materials that can be easily shaped, such as heavy Canson sheets, paper, wires, or clay. If you have the patience, you can experiment with gypsum or paper mâché.