Permitting can take forever depending upon your area, material/appliance costs & availability have been fluctuating, and you'll likely need some good protection depending upon where you decide to build.Great news is that it's still pretty affordable and looks like a great alternative to a standard home.

There are many reasons for climate fluctuations.

However, as J Scott pointed out, if bank fails to have adaquate assts, their required reserves fluctuate up and down.

While you don't deal with the risks of the paper market, except for the price fluctuation, you do need to keep abreast of what's driving the price in order to be ready to exit PM in order to move your wealth into the next asset\commodity bull market\ bubble.

Interest rates fluctuate, but they're around that 4.2% number.

Cap rates fluctuate.  

Commercial properties tend to cash flow higher than residential but we are still talking 5% cap rates.Also keep in mind currency fluctuations can impact your returns.

These statistics fluctuate and data can be misleading.

This is more flexible but also adds more complexity since the value of the shares will fluctuate over time and that needs to be monitored and calculated every time an investor joins or leaves the fund. 

There is a demand for housing regardless of interest rate fluctuations.