Ivy gun is strong :3

Buy in order or regen first if hard to survive (2500$)

Again in order to survive more with lifesteal and debuff ennemy with the spirit items (11250$)

Tesla <3 (Titanic for more bullet and Escalating for tank)
Not enough space for Intensifying ? Buy titanic first (if a lot of money buy siphon cause strong and tank) (29250$)

Siphon give so many free HP
Remove Extra regen and extra stamina to siphon et leech, headshot booster for lucky shot and slowing bullets for vampiric burst) (51300$)

If you don't have any flex spot, try to have the items in those order (those are the items you can buy cause they replace previous one or are upgrade)
If you have space, just buy in order above