Hello there,
First of all, welcome to the team building section of PC, i hope that i can be of some help to you.
First of all, we need to know what sort of movesets you are currently running and if you are looking to challenge other players online, or are you just going for the elite four?
Also what IV's, natures, abilities and EV's do you have in place for your team? if you are unsure of what this means then i'll explain that to you or you can use this site or Bulbapedia to look it up yourself.
If i was to use this exact team online i would perhaps use the following set ups (other people on here tend to want to change your entire team so i'm going to stick with the team you suggested and give you some options on how to use them effectively)
Scrafty:
Ability: Moxie
EV's: 252 HP, 252 attack, 4 def
Nature: Adamant (or Impish if you want to be more tanky)
Item: Leftovers (or Sitrus Berry)
Moves: Poison Jab, Dragon Dance (or Swagger), Hi-Jump kick (or drain punch for sustain) and Knock off
Scrafty is a pretty tanky pokemon so you'll have no worries taking hits, if you wanted to go all out tank you could swap the EVs to 252 hp, 130 DEF and 126 special defense. Poison Jab will deal with your 4x fairy weakness, dragon dance will allow you to become more powerful and outspeed more pokemon, drain punch and hi-jump kick for STAB damage and coverage and Knock-off for STAB and removing your opponents items.
Gastrodon (A personal Favourite)
Ability: Storm Drain
EV's: 252 HP, 126 Def , 130 Special Def
Nature: Modest
Item: Leftovers
Moves: Scald, Ice beam, Earth Power (Or Stockpile), Recover
Gastrodon can be quite the tank, with a great typing and only a 4x weakness to grass, Storm drain allows you to gain a Spec. Att boost when targeted by a water based attack, Scald allows you to burn the opponent to reduce their attack by 1/2, ice beam takes out our grass weakness and you can either go Earth power for coverage and damage or stockpile for tankyness. Recover is there to lay down the pain by keeping Gastro nice and healthy
Gallade
Ability: Justified
EV's: 252 attack, 252 Speed, 4 HP
Nature: Jolly
Item: Galladite
Moves: Knock off, Drain Punch (or Psycho cut), Rock Slide, Poison Jab
Knock off will kill off our ghost weakness, Drain punch is there for sustain, however psycho cut is also useful for high crit chance, Rockslide removes our flying weakness and is good coverage, and poison jab deals with those pesky fairies we have weaknesses throughout the team with.
Rotom-W
Ability: Levitate
EV's: 252 def, 252 special defense, 4 HP
Nature: Modest (or Calm)
Item: Leftovers
Moves: Will-o-wisp, hydro-pump, volt switch, dark pulse (or discharge, or Hidden power fire)
Standard Rotom-W set up, uber tank, to breakdown any attackers.
Dragonite
Ability: Multiscale
EV's: 252 speed, 252 attack, 4 hp
Nature: Jolly
Item: Leftovers
Moves: Dragon Tail, Extreme speed, Iron head, Roost (Or dragon dance)
Dragon tail will allow you to get rid of a bad match-up, Iron head is going to smash Rock, Ice and fairy weaknesses and extreme speed is going to get you that KO if the opponent s low health.
As for the final pokemon, i recommend Forretress (its steal and bug typing is VERY good)
Forretress
Ability: Sturdy
EV's: 252 Attack, 252 Def, 4 Hp
Nature: Brave
Item: Custap berry
Moves: Stealth Rocks, Gyro ball, Explosion, Rock slide (or Earthquake)
Ok this pokemon should always be your starting pokemon in battle, why? because its got stealth rocks, stealth rocks will limit your opponents switching of pokemon by causing damage to them when they switch or send a pokemon into battle, this also has an advantage for you as Forretress is 4x weak to fire, with stealth rocks up, fire types will take 2x damage from stealth rocks (4x if they are fire/flying), this will make an opponent think twice before sending a fire pokemon in on you however, if they send a fire pokemon in straight away, we can set up our stealth rocks and if they use a fire move on use, we are guaranteed to survive thanks to Sturdy ability, now what we then do is use Explosion, because we have a custap berry as our held item, it increases the moves priority by 1 stage if we are in red health (which we will be as we'll be on 1 HP). this will knock us out but also deal MASSIVE damage to our opponent, and likely take them out with us. (a personal favourite of mine).
I hope that helps you with your team building, any questions just ask :)