I played a steampunk, construct focused character in Kingmaker and had a ton of fun. That game was convenient for a construct builder though, since we had a) tons of down time, and b) an absurd amount of money. The GM also trusted my system knowledge, so I was able to build some of my own constructs, which was hugely helpful at early levels when other constructs were less accessible, as well as later when my early constructs started needing upgrades. You'll definitely want to talk with your GM about working with you on this sort of character concept, because construct builders are very difficult to pull off with the rules as-written. It might take a while, but once you have your robot army to command it is so completely worth it.
The construct rider alchemist does look hella cool though. Getting craft construct for free at level 4 is really good. Plus you could have a freaking fire breathing robot t-rex, and I mean... come on. Who doesn't want that.