Here in Hawaii land values have far exceeded building values for several years on most older properties. I access the assessor's land values AND contact local realtors for comparable selling prices of vacant land. Most times between the two sources a reasonable allocation can be made, and reminder, a reasonable allocation is what's required in lieu of absolutes as far as income tax return filings. When land values exceed the combined purchase price of land and building, I research for a comparable building value and use a ratio to allocate value to building and land. Due diligence and clear workpaper on how the numbers were derived are essential.