Doesn't have to be competitive really just cool. Also the summoning idea I don't get can you summon an extra 1k points say for argument sake. Any ideas for list building appreciated just no allies just dirty nurgle
You can, but it'll rarely win you the game. Theoretically you can summon units to (next turn) summon more units and so on and just drown the board in daemons, but:
1) Unlike Tzeench, you lack a psyker available through the Malefic Primaris (the only power you can garuantee getting)
2) You lack a troops choice psyker, so have far fewer warp charge to play with
3) Nurgle stuff is damn hard to remove in the first place so just double down on toughness
Summoning is a nice 'tool kit' power for daemons - lacking (for example) the options for melta bombs on your 'sergeants', being able to pull a pack of screamers out of your ass on demand is priceless. Summoning daemons to fill tactical gaps as they occur is very useful - but not an option if staying purely devoted to one god from the pantheon.
Nurgle units, as Reavas says, are ridiculously tough. Their most important power is Shrouded - +2 cover save which stacks with other abilities - and because you're not fearless (even though you have many of the positive bonuses thereof) you can go to ground.
if you go to ground behind a ruin, or a wood, or even just another squad, you get a 2+ cover save. Nurglings have 4 wounds each.
If they're dug in on an objective in a ruin, three nurgling bases are less than the price of a squad of Imperial guardsmen, and are about as hard to kill with ranged gunfire as a full terminator squad. Worse, if (as noted) you give them Feel No Pain from a herald.
Essentially, the pure nurgle units do the following jobs:
Nurglings - deploy on objectives (in your deployment zone or by infiltrate) in cover and go to ground if anyone looks at you funny. Their job is to survive the first couple of turns and just farm tactical objectives for victory points for a minimal cost outlay. Take minimum sized squads, either in 'spare' troops choices or as a cheap tallyband with a Fecundity herald.
Plague Drones - aggressive assault units and icon bearers. They're damn good in a fight, and fast - so deploy forwards and zip up the board as fast as you can. When the reserves start arriving, they provide the icons in your opponent's half you can deploy onto, and then provide your decent assault units. Plaguebringers (the unit champions) are surprisingly nasty in a fight; combine a greater reward, plague banner and venom sting, and they can offer a poison 2+, AP2, master crafted, instant death attack. Even pretty powerful characters will steer the hell clear of that.
Plaguebearers - the 'wave II' infantry. Deep strike them in up-board - they're too slow to footslog. Drop them off icons held by plague drones - or off icons held by other plaguebearers (note that unlike teleport homers, chaos icons have no provision requiring them to have been there at the start of the turn!). They drop in, shuffle over to an objective, capture it and (once again) go to ground. Unlike nurglings, they have a hope in hell of beating off an assault unit so can be used more aggressively. Big units are good, and getting the charge is critical - so use the cavalry to screen them, not the other way around. Plague drones on the charge go from 3 attacks to 4 (plus the odd hammer of wrath), whilst big mobs of plaguebearers double their punch on the charge.
Heralds of Nurgle - 90% of the time, mobile Feel No Pain generators and biomancy/plague buff generators. Attach to big plaguebearer units for best results. You can also get bonuses with Plague Drones - heralds are slower, but if you have a 'conga line' of drones, the herald can easily stay in coherency for a turn or two, and Feel No Pain can really tip an early fight. Equally, a cheap Tallyband (7 x 3 nurglings, Herald with Fecundity) costs virtually nothing and provides a daemonic incursion core that gives you enough feel no pain nurglings to invest (infest?) any local objectives with one or more pack. The relics you can take are amazing - the Grimoire of True Names is infamous, but Grotti The Nurgling and the Doomsday Bell are just as good, and a Herald in a big plaguebearer pack with one or more other heralds and a champion is probably the safest place to put him.
Great Unclean One - Shoot me! I Dare You! This guy is a big distraction. Stick in reserve, deep strike in (make sure you have an icon! he's too expensive once equipped well to risk a mishap) and get aggressive with him. Take 2 greater rewards, mastery level 3 and biomancy and force your opponent to shoot at the toughest non-superheavy model in the game or be squashed by it. Instruments of chaos one plaguebearer packs are useful here - that way, 2 plaguebearer packs give you 3 shots at bringing the great unclean one in at the first opportunity.
Daemon Prince Of Nurgle - always, always wings. Shrouded + Jink is a 2+ cover save in the open. Telepathy is nice since it's the only access to it nurgle has - and with the Doomsday bell's -1LD, psychic shriek is extra nasty.