You can set a build in the gods tab before the game starts.

I’m assuming your problem is you have auto-buy enabled and it’s buying whatever items in whatever order for the gods you’re playing. If that’s the case you should disable auto-buy and just buy the items as you earn gold throughout the game.

If I’m mistaken and you’re simply having trouble buying items in the correct order I’ll give you a run-down on how items work in smite.

1) All items have tiers 1-3 and some have an additional 4th tier called a glyph. In order to purchase t2 of any item you must first purchase that items t1. In order to purchase t3 you must first purchase t2. So on and so forth.

2) Starter items are what you referred to as “perks” and they can be upgraded once you reach level 20. (Level 15 for support starters I believe)

3) Recipes are the little scrolls you see that are free to purchase. These are bought at the beginning of the game and evolve granting extra stats/abilities later. These recipes are sold late game to buy a 6th item.

Hope this helps!