Geez how do you theory craft your own build
Its so complicated
Pick a skill you like, aim for 4k+ HP. For hardcore, add solid defense. Something reliable like armour, phys conversion, something that reliably reduces incoming damage. On softcore, you can gamble with evasion + dodge (aka the Acrobatics keystone), i.e. zero damage reduction.
The rest is just finding out what passives and other stats scale your skill's damage most. The skill description (projectile, AoE, duration, etc.) will tell you most of what you need to know. The more specifically targeted nodes (axe damage vs two-handed physical weapon damage) will generally be worth more, but you might have skills that benefit more from a less specific node, like Essence Drain. The skill description makes it sound like you should concentrate on chaos damage and duration, but projectile damage will increase both the initial hit and the damage of the DoT it applies, so it's best to grab the juiciest proj. dmg nodes you can get.
Most skills are less 'complicated', a small minority (Righteous Fire, Explosive Arrow, a bunch of Unique enabled builds) take more thinking than that due to their mechanics and how they apply damage. Bookmark pathofexile.gamepedia.com for those and to scope out uniques and such, invaluable resource.
A 90 point build will be around lvl 75 or so, including all the side-quest passive points you can get. I aim to have all the traveling done at 85 points spent.
Last but not least, try to be as efficient as possible when you route your path on the tree, but this should be obvious.
That's all there is to it, really. After you've done it a couple of times, every kind of build, wether it be a melee attack or spell based build, crit or non-crit, support, minions, traps, etc. will kind of look the same, because for the most part, they are. They can get so similar in fact, that you could just swap out the skill you're using and still be just as effective.
