Guild Wars 2

I am crafting my viper ascended armor and i was wondering…

Is it cheaper to craft it as rabid(or any other stat set) and then convert into viper or directly viper?

Look at the ascended crafting table of gw2efficiency and compute the values for yourself:
https://gw2efficiency.com/crafting/ascended

As far as I see it, there is currently a difference of about 8 gold between directly crafting Yassith’s (Viper) and the cheapest other (Ferratus’). But the Viper’s Intricate Gossamer Insignia required for the conversion costs about 9 gold itself, so it’s cheaper to directly craft Yassith’s.

Note that GW2efficiency doesnt calculate the cost for Fulgurite (as the mats are account bound). HoT stat ascended (except marauder) require jeweled damask patch instead of damask patch for non HoT stat ascended, which uses 25 fulgurite each.

Now, if you have tons of obsidian shard, airship oil, auric dust and leyline spark, you can just make Yassith’s directly. If you don’t (especially obsi shard), it’s better to convert from a cheaper set.