I can see how a designer might relate to this. As a web developer / site architect, though, this has not quite my experience. For people in my line of work, our letter might read more like:
Dear Mr. Architect,

Please design and build me a house. I am not quite sure of what I need, so I have delegated the project to my three year old son Timmy, who is very smart for his age and is cute as a button. Timmy informs me that the house should be "really fun" and preferably blue. Timmy likes blue.

Brainstorm several floorplans with Timmy and then bring them to me so that I can randomly combine them in a totally nonsensical, structurally unsound, configuration that makes perfect sense to me, but will cause my dinner guests to go permanently missing.

Also, don't worry if safety and zoning ordinances are overlooked in construction of the house, as I want it to be as inexpensive as possible. Although I am not willing to pay for electricity or gas, or even a generator, I would like a fully functional kitchen with gas range, refrigerator and microwave oven. If you could figure out a way to get our toilet to flush without plumbing, that would be great too. Just be sure to make the kitchen blue. Timmy likes blue.

P.S. We will be totally revising the blueprints once construction is finished. We hope that this will not add to the cost of the house and that you will do any additional construction for free.