This resource will figure out how much soil or mulch you will need. You do need to know the measurements of the area and the depth you require.
If you are mulching... a 1-2 inch depth is usually adequate.
How high you build a planting bed will vary greatly. Your goal is to provide a raised area that water will not stand or drain to. 4-6 inches high usually accomplishes that. Be sure not to cover up the weep holes around your brick house. If you cover the weep holes water could get into your home.