Are the following sentences parallel?
Not only was it raining all day at the wedding but also the band was late.
Not only will they paint the outside of the house but also the inside.
They are parallel in that there is a coordination in both with but and modifier not only present at the start of the sentence, but the coordination is not of like categories. In the first there is a coordination of clauses, and in the second of noun phrases.
[Not only was it raining all day at the wedding] [but [also the band was late.]]
Not only will they paint [the outside of the house] [but [also the inside.]]