I am currently writing a book in English.
My language abilities I would judge as very good. I studied in the UK and work mostly in English.
However, I am not a native speaker and thus my English is not perfect.
I require proofreading mainly with respect to grammar and commas, less in terms of formulations and wording.
In order to assess the work, I provide a large sample of the text I have already written.
It is about 30% of the total volume of the book.
I will finish the book during the next 2 months but the work could already start.