Use a folded boat if you have one.

Does the roper get to use the Reel on each of its attacks if they hit?

Volo's guide said that they are common pests to hill giants but don't ropers only live undergound?

Our party recently encountered a Roper and we had some real fun with it! We found the Roper fishing near a stream deep inside a cave system. We knew from our nature and history checks we'd be in some trouble if we decided to take it head on so like a bunch of munchkin PC's we decided to lay a trap....

Our barbarian donated her "Grek tentacle bed roll" and our bard illusionist and gnome tinkerer began shaping and fashioning  the tip of it into a fish looking shape (including fins) and forming a belly to contain our payload. Spells of mending were used to add dorsal fins etc. Among our party of less-than-lawful hero's our necromancer "granny" who donated half a dozen poisoned muffins to fill it's belly with and the rest of our crew donated everything from a vial of alchemists fire to regular run of the mill poison to fill it up and give it some ballast.  Once we had our Trojan fish assembled our bard used prestidigitation and illusion spells to make it smell, look and taste like a nice sized fish and then we tied a small string to the tail and headed off to put it afloat.

Our resident locksmith and barbarian snuck down upstream of the monster and began floating the fish in the river and eventually had to toss a pebble beside the floating trap to get the Roper to take notice. The roper ended up buying in on our decoy and eating the entire mess.... a few moments after chewing and swallowing it the Roper began foaming at the mouth releasing poisonous and putrid belches of containing clouds of flaming indigestion. Not too sure what our alchemist put in that sac but I'm guessing some of those chemicals really didn't mix all that well.  

Cackling like lunatics our heroes ran for all they were worth back away from the worst case of acid reflex you can imagine and hid in an alcove listening to the  Roper lose it mind! This may in fact be the first documented case of Roper fishing ever recorded.

Now this isn't the end of the story but I hope I've given you some ideas on how a party of level 4's can overcome this terrifying monster.

It's not like other monsters. It has: snake arms.

Quote from ShaydyCharacter >>

These things aren't immune to being shove prone hmm, though they are strong and impose disadvantage on strength checks with their tentacles, so succeeding in shoving them over would be a challenge. I'm spitballing here, but if you have no other options, a raging Barbarian or enlarged Fighter with athletics prof could shove it over and grapple it, giving it disadvantage on all its attack and everyone advantage to hit it, or cancelling the disadvantage on roped folks. This will only cancel the advantage on its bites if you're roped, but it'll make it harder for it to re-rope people too. For it to even get up and flip things back, it would have to use an action to escape the grapple, wasting a turn. It's... not the best way to deal with a roper, but if you don't have any better alternatives, it can make it a lot easier to handle.

 Just have the barbarian pick it up by the tentacles and either throw it across the room or smash it on the ground. Or use a vacuum.

Ah yes a challenge rating of 5 for an enemy with 20 ac, 4 grapple attacks, and an attack range of 50ft.

no

If you really want to be a mean DM, have the roper attack from the ceiling of the cavern 40-50 feet up from the ground, using all four strands. If two or more strands hit the target, the PC would only be able to make one strength check per round to try to break a strand, which would almost ensure that character ending up getting a close up look at the stone teeth of a roper. If all four strands hit, that is likely a certain trip to digestive juice city. Even a tier 2 character would have difficulties surviving if it took 22 HP of bite damage every round and had disadvantage (no save) each round on strength (grapple breaking) checks.

On the other hand, if you have a party member with lightning bolt or fireball at the ready, just blast the thing and watch out for where it falls. Fireball doesn't care about your armor class!

Great created 10/10

No when you're grappled you are incapacitated which means all you can do is try to break the grapple, you can not attack at all.

you are not incapacitated when you are grappled. I have no idea where you got this idea.

Read the grappled condition it states that you are incapacitated

I wouldn't nerf it completely because it makes sense that they would have some solid defense to survive in the Underdark (some crazy powerful mobs down there). I would make it so if the pc attacked its obvious weak points where there is no armor (eyes, inside the mouth, or even better if they could somehow hit something inside the creature completely) the monster was easier to hit (that way it makes sense and rewards players for thinking tactically instead of just charging). The easy way to beat it (besides the obvious aoe spells) would be to make a Molotov cocktail using an oil cask or booze with a cloth and toss that at it or possibly inside its mouth. That destroys all the tendrils and keeps destroying them as long as the creature is on or in fire along with doing minimal damage to the creature. Now it is an easy target with no way to guard its weak spots and the fire makes it easy to see (removing any penalty from players who do not have dark vision and possibly allowing all pc to have advantage on attacks because it is super easy to see). Alternatively, just run away since they are slow af or try to reason with it. They are evil but not stupid and so if a pc dropped a ton of food on the floor then ran that could easily be enough to deter it since it knows that it might not be able to catch pc without a fight which burns calories and leaving food on the ground is a good way to have something else steal it but it would have to be a decent amount of food for that to work imo. If a pc is going into a place that has mobs which are too powerful for them currently the dm should warn them somehow (use your imagination and make it obvious/blunt but do not force them or stop them from going in anyway). There have been a few times where the pcs have surprised me and come out on top despite the fact that they shouldn't have (sometimes luck pulls through). There have been a lot more times where the pcs all died but they learned when everything is telling you something is a bad idea it might be wise to listen and that freedom for the pc to do whatever they want is what makes the game great.

Quote from Deathsbestman >>

Read the grappled condition it states that you are incapacitated

 No, it says that the condition ends when the thing grappling you is incapacitated. All grapple does is set your speed to 0.

Does a roper count as being made of stone for the purpose of the shatter spell?

It does not. It is not made of stone. It only looks like it is.

If re-skinned and a few modest tweaks, this could make for a good kraken-esk sea monster for a lower level party.

im level 6 fighting this alone

Made a variant in my homebrew where these guys look like corpses.  Then unleash a scene from The Thing when they search them.