Welcome to the Hive

Tyranids are in a tough place as it is as they do not have a power Codex (as say Tau or Eldar) but with the right builds they can successfully win games. It's a challenging army to master as it punishes mistakes more than say Space Marines but it's satisfying to win with and more than capable of giving the top tier armies a run for their money (I myself have a win:lose ratio of 4:1 against my Tau friend with Nids).
Now that that's out the way, let's get on with what models to collect. At this points level he can afford to invest in the Hive Tyrant with Wings and Twin-Linked Devourers. Some people (such as myself) like to put on Electroshock Grubs for Haywire as Tyranids have problems dealing with AV13/14 (with Smash being nerfed, the only reliable sources are Carnifexes with S9 hits that need to get into Close Combat and Warp Lance, which has it's problems being a Psychic Power).
The problem with the Tervigon I find is that it's not going to do much aside sit on Objectives and babysit the Termagants that it's spewing out - and it's quite a points sink in a small points list, on top of the 120 points you're shelling out for the brood of Termagants so you can take it as a Troop choice. On top of that, it's not always guaranteed to create ore babies (one game I had, I rolled a 2+2+1 on the first turn! Talk about a letdown) and when it dies (as opponents will likely target it) it will make the Termagants go berserk and fall back half of the time, not to mention it will most likely kill a few Termagants it was babysitting due to Synaptic Backlash). For troops choices instead I would invest in Warriors as they have Synaptic Creature so won't require babysitting and can invest in long range weapons (Basic Biocannons) so can sit on Backfield objectives while still causing a few problems to infantry. I personally would invest in a Barbed Strangler per group as it causing pinning and leave it at that, however, a Venom Cannon, while having a small blast and no pinning, does pack more of a punch, can hurt light vehicles, so your friend needs to decide which is going to be more useful in his meta. They both cost the same, so (if your FLGC allows it) he can proxy them before making a final decision over which to take.
With the Hive Tyrant as mentioned above and the Warriors as suggested comes to 440 and satisfies the
FOC - which means we can invest in the wings. I would start off by adding a Hive Crone as it provides more
AT with Haywire Tentaclids and S8 Vector Strikes (and helps the Hive Tyrant by presenting another
FMC for opponents to deal with).
I would then load up on Gargoyles. Two squads of 12 and 13 Gargoyles will give your friend the 'swarm' aspect of Tyranids as well as provide more targets for the opponent to deal with..
So to summarise, I would use this list for your friend at 750 points, basing this on a vehicle meta:
Hive Tyrant
-Wings
-Twin Linked Devourers with BLW
-Twin Linked Devourers with BLW
-Electroshock Grubs
=240
Tyranid Warriors x3
-Barbed Strangler
=100
Tyranid Warriors x3
-Barbed Strangler
=100
Hive Crone
=155
Gargoyles x12
=72
Gargoyles x13
=78
Total = 748 (with 31 models split between 6 units and having to fire Snapshots at two of those units).
If your meta is more infantry based, then a Harpy in place of the Hive Crone and upping the number of Gargoyles in each unit is more than acceptable. (14+15 with a Stranglethorn Cannon Harpy, 14 in each for a
HVC Harpy)
EDIT:
As to where to go from this...you're friend is going to want to collect Tyranid Dataslate: Rising Leviathan 2. This grants you access to the well known Skyblight formation, which on top of
FOC, gives you another Winged Hive Tyrant, Hive Crone, two Harpies and three sets of Gargoyles, with the Gargoyles having Objective Secured like troops, but having the chance that when wiped out, can renter the battlefield on a 4+! That is pretty good

Perhaps the first buy if you increase to 1000 points is another Flying Hive Tyrant, for more Synapse and helping the first Tyrant out a bit by again, more
FMC to deal with.
Other worthwhile investments are Venomthropes and Forge World Malanthropes as they provide Shrouded to an army that desperately relies on cover as well as Zoanthropes for Psychic powers and Hive Guard for light tank killing. Heavy Support in general are all good choices to go with (except the Trygon, which requires too much investment for it to be semi-viable).
I hope this was informative and I wish your friend all the success with Nids!