This depends very much where you live. In some places with very expensive property markets the structure can be as low as 20% of the cost of a home (a typical downpayment amount) -- conversely, with low property/land values, the quality of the building itself can be most of the value.

A side effect of high land values is that the relative cost of teardowns/rebuilds is much lower, so you tend to see more replacement of the buildings themselves unless there are other regulations in place blocking that.