As an example, you could try to replicate the Kölner Dom as a pure gold structure. The building has an estimated mass of about 300000t, and is mostly built with Trachyte, which has a density of 2.78g/cm³, or 2.78t/m³. Accordingly, the building therefore has a stone volume of about 108000m³, and with a density of 19t/m³ for gold, it comes to an amount of gold of about 2.082.733t The price of gold right now is 47.000€/kg, or 47.000.000€/t. The material costs for your gold cathedral therefore is about 98 trillion €.