Patent drawings are not for the faint of heart. I did some a while back (in my cad days) and lost my a$$ on the job. They are very specific on the style, paper, text (font), etc. The drawings actually took me far longer than expected (came back 8-10 times and not due to anything other than not "looking" they way they wanted them). They may not even tell you what needs to be corrected (they say you need to know). I learned that I will not be doing patent drawings again anytime soon. A few pieces of advice...do you homework. Get ahold of the patent office you will be submitting to and see if they have a book of standards they want you to follow. Bid the job about twice as much as you think (you will be revising it many times for the smallest of corrections). Good luck.
Scott