I won't give this a -1 Illiterate, but really the spelling and grammar are painful. There are misspellings that would be found if you simply pasted the text into Word with spell checking turned on. Also incomplete sentences, which again would be found with Grammar checking.
You also need to pay attention to continuity. In chapter 3 the letter from Gringotts refers to "Severus Octavian Snape", while in Chapter 4 he calls himself "Severus Tobias Snape".
The plot is interesting enough to keep me reading though.