So a fanfic with 20+ chapters but with the minimum requirement of 60 words. Hmmmm difficult difficult
There are a ton of second chance HP fanfic on fanfiction.net and ArchiveofOurOwn. Most of them are Harry goes back to year 1 in Slytherin or something like this. Never saw any reincarnated as Severus Rogue tho but with AO3 filters it shouldn't be too hard to find at least one. You could ask /r/HPfanfiction/ on Reddit. Also on that subreddit there is already a ton of people seaking recommandation for second chance HpFanfic. Hope you can find what you look for.
I don't know if you specifically want a Snape one but this one has a guy from our world reincarnated into the Harry Potter world. He instantly decides to become powerful and studies a lot to learn more magic. It's pretty good. https://www.fanfiction.net/s/13361607/1/Rebirth-in-a-Magical-World It's got 200K words
half blood emperor has a si as snape but the fic is sadly dead. died just when it started getting to the good parts too.
Well, dunno if this'll help but here are some fanfics and original works that i enjoyed reading. 1 - Forged Destiny is an RPG take on RWBY. With over 1 million words its simply said a beaut. 2 - Mother of Learning is an original story and the lesser I say about it the better because words fail to describe how well written this fic is. 3 - Oddity is a naruto self insert fanfic which is nice. Not comparable to the first two recs but the latest chapters have left me with a shiver running down my spine and goosebumps on my arms. 4 - Going Native is a dragon ball self insert fanfic with a crossover into the dc multiverse. The fic is quite well written and is definetly worth a read. 5 - Skywalker Resurgent is a star wars self insert fanfic that brings back a lot of good memories if you're part of the generation old enough to remember and appreciate the greatness of the original star wars triology. 6 - The Muggleborn Conspiracy is a harry potter self insert fanfic that was pretty awesome but the recent chapters have seen a little drop in quality. Well, either that or I simply don't like the direction in which the author is taking the plot. :/ happens from time to time. 7 - Y'know Nothing Jon Snow is a pokemon self insert fanfic that is wonderful. It's rare to see a pokemon si that isn't dead as well as well written at the same time. 8 - Sacrifice and Subjugation is a pokemon fanfic that one would love if they're into grim dark realities in the pokemon franchise. 9 - Departure from the Diary is a harry potter fanfic that one should read if they're into the trope of gender bending the villain and making the villain and the heor an item in a plausible manner. 10 - Carl the Jumper is an example of a somewhat well written jumpchain. Unfortunately the world the author has taken the Mc into currently isn't one that I particularly like so I havent read this one in a bit.