Most guides I've looked at for Tristana feature the standard Beserker Greaves/Dorans Blade/Vampiric Scepter as early first buys.

However, since I've noticed that Tristana benefits greatly from her Phantom Dancer/Infinity Edge combo, and her damage scales greatly (even more than other AD carries it seems like) when you get the combo, is it worth it to race a Phantom Dancer then Infinity Edge without buying Dorans Blade and Vampiric Scepter at all in the beginning?

For example:

Spawn First buy: Boots 3 Pots
<then>
When enough gold, buy Zeal and Beserker Greaves
<then>
Buy rest of items to complete Phantom Dancer

Why PD instead of IF at first?

Because PD is cheaper and you can get it earlier. It seems to me that combined with the low cost, the attack speed and the crit stats, that the item stats exceeds the attack damage and crit stats from IF.

Can buying a PD early help snowball Tristana earlier, and thus lead to a more successful item build and game damage?

That is my question. Do you guys agree? I bet most of you will disagree, mostly because of the sustain that Scepter and Dorans Blade give. However, like i said, Tristana seems to benefit a lot more from that two item combo, and getting them early could really give her a head start in her damage build. Plus, with the money you save from the low cost of PD, you could always just buy health pots to make up for loss of sustain.

Tristana has AS so she would prefer to get ad to optimize damage.

I've gotten away with building IE last, but it was a gimmicky match on the PBE. I was killing it in mid lane, rushed Shiv, went new BotRK (the one that was 30% of your AD), PD, LW, IE. I guess anything can work if you know how to read the situation you're in.

I actually tend to build IE very late, since it's not actually that great an item. I usually go Bloodthrister->Phantom Dancer->Last Whisper->Infinity Edge->Defensive Item/second PD/Shiv. Infinity edge weakens your early game until you get a Phantom Dancer because it takes longer to build and relies heavily on criticals, which are also reliant on attack speed. Building a Bloodthirster first gives you high sustain and AD, which is much better pre-Phantom Dancer, then you can either choose to go for higher damage with the IE or go for penetration if needed with the LW.

Of course, getting the IE first can still be good, but I usually find Bloodthirster to be the better early purchase.

All attack speed bonuses from leveling up are added to item bonuses, not multiplied off of by them. So you start with 100% attack speed at level 1 and end with around ~150% attack speed at level 18 - as such, the attack speed bonuses from Phantom Dancer end up being only about 66.67% of what they display as the game progresses. Also, attack speed is sort of the retarded cousin of all the AD attributes: damage, critical strike chance, and armor penetration will all see a solid bonus to your damage when you're harassing or kiting enemies, were you generally have to sit still for attack speed to count. As such, it's generally not advised to rush attack speed, unless you have really powerful on-hit effects that merrit doing so.

Also, Tristana has an attack speed steroid - which also rides off her base attack speed, and doesn't multiply item attack speed bonuses. Attack speed has no synergy with attack speed steroids in that sense - but does work rather well with things like attack damage and critical strike chance.

Beyond that the reason you'd rush items is for the goodies from completing them. Phantom Dancer's unit collision is nice, so is the movement speed - but neither are that core on an ADC, at least not right away.

It's great to experiment with builds, and probably doesn't matter much what order you get the items until you're Elo gets to the upper levels - but the above is mostly the reason you'd get Infinity Edge first, and why rushing Phantom Dancer generally isn't the best idea - unless you're Vayne (silver bolts and the final hour AD steroid) or Kog'Maw (extra range and that health and armor shred on-hit).

You wrote "why PD instead of IF at first?" Isn't it suppose to be IE instead of IF? Anyways back on subject IE is better since trist already has a steroid. Her Q.

Playstyle choices. Most trist players won't engage unless. Is ready, so why rush as? I do either i.e. or t first depending on how well i am doing, then get zeal, and i usually don't upgrade to pd until i have ie, bt and last whisper or botrk

IE is generally the best item to rush on trist as she's a very auto attack reliant champ.
Other adcs get away with rushing bloodthirster for sustain as they have AD scaling on their skills, which trist doesn't have.
To get the full effect from phantom dancer you need a bunch of attack damage first to make the extra autos hurt, and early zeal is ok for the movement speed and as/crit chance, but phantom dancer is a little too expensive while not giving much if you don't already have ad.

Think getting damage would be more important because of Trist's q which is a very strong attack speed steroid. Something like a Infinity Edge or Bloodthirster would benefit her much more IMO.

With AD Carries who burst, I emphasize Bloodthirster.
With AD Carries who mainly auto attack, I emphasize Infinity Edge

With AD Carries who burst, I emphasize Static Shiv
With AD CArries who mainly auto attack, I emphasize Phantom Dancer

It doesn't matter in the long run which item you get first, but you definitely need to get the item's counter part: IE and PD, BT and SS.