How to make my own builds?

Skills - grab the ones that synergize, supports should be damage.

Passives - usually straight to the top of the tree with only minor deviations. If you're playing off-class, you might go around the inside towards that classes starting area. Generally do not grab defence in campaign - a couple of points towards life recovery or regen might be reasonable at the start. 

Gear - your currency should mainly be spent on weapons and jewelry. Focus flat damage, life, and resists. Save up any chaos res gear to swap to it in a3. 

Socket and quality your weapons. In act 2 your build is basically take all decent defensive and offensive notables by your starting area. Get your first two ascension points if you haven't.

I've been killed by act 2 boss even after hundreds of hours but it's solvable.

If you have to ask, you'll never know.

Use Path of Building and your knowledge of items / skills in the game to put together something that synergizes well and gets you ahead of the damage / defense curve.

And when that fails realize that people who spend all day every day playing the game and have thousands or millions of followers to theory craft and challenge their concepts are probably going to have a better starting point for builds.. Especially after so many seasons have elapsed for people to discover the good gear / skills.

PoE 2 builds are a lot more straightforward than PoE 1 because the skill design is far less flexible. For the most part, each skill is designed to synergize with a few other specific skills, and you cannot freely mash together a rotation that mixes multiple “skill groups” together because the interactions just aren’t there — this is especially true of attack/weapon skills. Don’t fight these pre-determined archetypes… just pick a weapon intended for your class and read through the available skills to figure out which ones work together. It should be fairly obvious. Ranger Lightning Arrow + Lightning Rod for example: drop rods then shoot LA for a massive burst of damage… but trying to mix them with gas/explosive/poison skills just has no beneficial interaction at all.

Once you find a strong combo of 2-3 skills intended to work together, start reading up on how to scale damage for it and path towards relevant nodes on the passive tree. The passive tree is a mess in PoE 2 so you’ll have to basically hover over everything in a large radius to find a few useful clusters.

I know you said you don’t want to use guides, but I would highly recommend visiting poe.ninja and selecting your choice of ascendency and main skill. You don’t have to look at or copy any specific player’s build for this to be helpful. Take a look at the Passive Heatmap to get a rough idea of how other people are pathing around the tree and which clusters benefit your build at all. Take a look at support gems and uniques that people are using and then decide for yourself.

One thing to look at when you pick your class is to open the skill tree and see what nodes are close to you. Synergies with what your class is good at is always a good start. If you have a lot of projectile damage by you, pick bows. Being a spear wielding ranger wouldn’t be good because so much of the spear nodes aren’t near.. and so on.

If you ever worry, just remember SO much in the game is capable of working, just less than others. Meta builds are busted, but there’s a guy that plays randomized builds on YT to do like gas arrow lich, spear titan, bone wall smith.. and all of them can kill the endgame bosses. They are 100% worse than like a poisonburst arrow, but they still are enough to succeed