present economy

The Philippine Institute of Civil Engineers is planning to construct its own building. Two proposals are being considered: (a) The construction of the building now to cost PhP 400,000.00 (b) The construction of a smaller building now, to cost PhP 300,000.00 and at the end of 5 years, an extension to be added to cost PhP 200,000.00 Which proposal is more economical if interest is 20%, depreciation is disregarded and by how much?