As the cloud of material collected, it probably was homogeneous, with a more or less even and random spread of different elements and compounds. The sun, at the center, collected most of the material - some rocky materials, but most of it was gas - hydrogen and helium.
As the cloud flattened and the first planetesmals collected, they were likely made of about the same material - figure 200 to 400 small bodies in orbit around a dark mass at the center. These smaller objects collided, some stuck together, and the number of bodies in the cloud began to fall, as the individual planets began to grow.
At some point, the sun was born - it's core heated to the point that it crossed the threshold of fusion, and solar wind began. At this point, the solar system had probably a few dozen planets, still swimming in a cloud of gas and dust.
Solar wind blew the lighter materials - gases, some ice to the outer solar system, and the 4 inner worlds stopped growing, as the material they were collecting was blown away.
And, the rocky cores in the outer solar system started collecting the material that was being blown by solar wind... Jupiter grew to the immense world we know today; Saturn, a little smaller, and much further out - Uranus and Neptune also grew. (There's a theory that a 3rd Neptune-like planet may have existed out there as well; but it's only a theory at this point.)
The cores of all the planets are likely somewhat the same - iron/nickel, at depth, with lighter silicates above that. If you could strip away the atmosphere of all the planets, the gas giants of Jupiter and Saturn would likely be 'super-Earths' - Jupiter may have a rocky core equal to 18 Earth masses; Saturn's core about 1/2 that, with Uranus and Neptune smaller cores still, but probably larger than Earth.
So... location is one factor in what makes a planet - Jupiter happened to be in the right place to collect a LOT of material that the inner planets weren't able to capture...