Joshmohr:
Today i was browsing deamons, when i noticed how similar they could look to the tyranids. Why not buy the plastic tyranids (Tyrant, Warrior?) and convert them into some more interesting looking models?!
Hazkar:
sure,you just have to make sure,i wouldn´t look to scifi
i plan to use a pyrovore as hellcannon
what are you planing?tyrant or carnifex as greater deamon of khorne?This snake like tyranids as slaanesh deamon?
Joshmohr:
i was going to use 3 Warriors as greater daemons of slaanesh… Or maybe just greater daemons. I’d add quite allot of green stuff, though.
Hazkar:
sounds interesting
keep us updated with some wip pics 
Snotling:
well, for me they look like sci-fi aliens, not like hellborn deamons. But I saw a deamon army on CMON with tyranids converted as insect daemons.
the plastic ghouls look like plaqubearers, you could convert them into some
snowblizz:
i was going to use 3 Warriors as greater daemons of slaanesh.. Or maybe just greater daemons. I'd add quite allot of green stuff, though.A Tyranid Warrior is about 1/3 - 1/2 the size of a Greater Demaon though. To small by my reckoning.
Joshmohr
Generally I'd advice against using Nids as Deamons. Nids look more "alien" (pun intended) than even Deamons do. I've yet to see a really good conversion that didn't still scream "Tyranid Bug".
If you think you can pull it off, don't mind me and my set ways. But mainly the Warriors are going to be too puny for a Greater Deamon.
Thorne:
Oh I dont know perhaps make it a inch or so taller wiht a greenstuff abdomen and build the chest up to a more humaniod type of chest and some long robes, Maybe a staff wiht a icon of slanesh or Tzench and it would make a pretty cool deamon prince/greater deamon, Id be more worried about how I was going to make a weapon of sorts than anything else and wings cause deamon prince or greater deamon gotta have wings, Would be kinda cool.