Creating a string of repeating characters is really simple in c#, however it is not in the obvious place you would look.  First I tried the String class, hoping there would be a static like String.RepeatString, and even looked in the StringBuilder class.  Eventually found it in a very logical place when you think about it, the String classes constructor.

String (Char, Int32)

So to create a repeating string simply use

String myString = new String('x', 12);

which will create a string of x’s 12 characters long.