Is an addition on investment home financially worth it?

[Jonathan Morgan]

I might turn my current residence into a rental property and move elsewhere. On average, 3/2 homes in my area rent for ~$700 more in my area than 2/1 homes. My current residence is a 2/1. I figure if I can add on a bedroom and bathroom to my house for <$70K, I will have a decent ROI when the home becomes a rental. Does this make sense, or am I missing something? I read online, in general, that adding roof onto a home is likely never financially wise. Quotes to complete the addition above, though, appear to be <$70K. I'm worried, though that these quote may be too good to be true.