Dear Kelly; 

Just a little note to say THANKS! for the work you did for us. 
We have been very impressed with the quality of your work, with your meticulous attention to detail. We appreciate your willingness to spend time with us whenever needed, to discuss our options and the progress of the projects. As we’ve said to you before, you possess a quality few other contractors we’ve dealt with possess: not only do you always show up for scheduled appointments, but you even show up on time. 
Good luck in all your future endeavors. You can be assured that should we again be in need of construction work for which we will be hiring outside help Kelly Construction will be our contractor of choice. 

Yours Truly 
Michelle & Peter