Hi Tarkowsky
Actually, "a too long sentence" is not too common a structure in English.
![Wink [;)]](/emoticons/emotion-5.gif)
I'd categorize "a too long sentence" not only as unnatural, but also as incorrect.
You can say this:
That sentence is too long.Or you can say this:
That is too long a sentence.
You can say this:
That is an overly long sentence.
You can also say this:
That is a very long sentence.You should
not say this:
That is a too long sentence.
The word 'too' is a special case. The usual pattern in this case is
too+adjective+a+countable noun
too expensive a car
too easy a question
too rosy a picture
too small a sample
too optimistic a view
too steep a hill
much too long a sentence