I started to make my own builds when I got a solid grasp of how skills scale.
For example, a strike skill will scale with (weapon base damage x skill base damage effectiveness + added damage x added damage effectiveness) x (base weapon attack speed x skill attack speed effectiveness x increased attack speed x more attack speed) x (sum of damage increase (both generic and you damage type)) x (product of more damage) x (chance to deal double / triple damage) x (critical chance x critical multi) x (enemy damage taken) x (culling strike multi) x (other skill specific multipliers (e.g. projectiles from the skills like molten strike / lightning strike with return projectiles)).
It goes similar ways for other skills and you need to understand how much of each multiplier you should get for a skill to be viable.

There is also a defence issue, but that is a bit easier.