Playful Parsing - What Modifies What?

I have been seeing this sign at street corners in Michigan lately and I can't help but play with the wording every time I see it. 

The first time I passed it, as I was repeating the words in my head, I couldn't help but wonder if the company would remove stains from pretty roofs as well.

[[ugly roof][stain removal]]

The more I saw and thought about the sign, the more I realized how many different interpretations are possible for the four words. And I do love having fun with bracketing paradoxes and parsing.

If I am having roof stains removed, I want it to be in a pretty fashion, not an ugly one.

[[ugly][roof stain removal]]

I'm pretty sure the following is how the sign is intended to be interpreted...
[[[ugly][roof stain]][removal]]

But this still leaves open the question of whether or not there is such a thing as a pretty roof stain?

Sign image found here
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