You've got it wrong. It's not really build-up, it's just another piece to the picture, another layer, and just some (in my opinion)pleasant and tolerable sound to add to some extent some sort of dynamic.
When I hear this, it makes me think of a man walking out of his house, down the cement path from his steps to the sidewalk, and continuing as he is amazed by his surroundings. Empty stretch of road goes on endlessly, with almost beacon-like beams of orange light coming from places beyond his range of sight. A white void or endless amount of cosmos or different reality, or lack there-of beyond in all directions but along the road, and the road itself. He continues on, nothing changing, and eventually he stops. There's no panic, there's no shock, and no horror. He's admittedly disappointed, but content to an extent, because there's nothing here, and because of which, no fear, no pain, and no end, but at the cost of joy, and any and all beginnings.
The Percussion toward the end, ehhh I can't really say. The first one that comes in, honestly gives it the same feeling as the percussion in one or two of my other songs that almost brings a happiness to it. The second one just adds some depth to it in my opinion. The chime-like synth adds a sort of eerie, angelic, and peaceful sound to it. The Acid synth, I feel goes well with the lower notes of the piano for the sake of it feeling more full.
I don't know, I think the reason you're waiting for the buildup so much, is the fact that it's as long as it is. If it were playing as a background noise, or if you only paid subconscious attention to it, you'd probably like it a lot more.