C# - Dynamic SQL

Over the last number of years I have seen a lot of code which has been used to generate lots of dynamic sql. There has always been one thing in common with the way that I have seen this be done. Typically the approach is to have a string and just directly append everything to the end of the string during a button press or some such from the interface. I have seen cases where the c# code to produce a dynamic query have been over 200 lines. It would typically resemble something along the lines of this.