At your height and if you’re used to riding modern geometry 29″ mtbs and a complete novice to pumptrack/skatepark riding. Don’t waste your money on a BMX. Even a 22″ wheel BMX or an XXL race bike is going to feel super unstable and twitchy under you. And contrary to popular belief BMX’s are far more challenging to manual and jump and even corner as well on than a 26″ DJ bike. Especially if you’re coming from large mtbs . You’ll also probably shit yourself when you find out just how poor BMX brakes are. A BMX is also not noticeably any faster than a DJ bike on a pumptrack at all it just feels a whole lot sketchier going the same speed on 20″ wheels and a 6″ shorter wheelbase. so long as you have suitably fast rolling tyres and are running around 70-80psi both wheelsizes roll on pumptrack asphalt just as fast.

If I were you I’d be looking for a secondhand DJ bike with around a 22″ toptube (often listed as L for long or large). There are literally hundreds of 26″ DJ bikes on Pinkbike for sale. plenty under $500. Trying to build something from frame up even with second hand parts would probably work out fairly expensive and if you don’t really know what you’re doing there’s a good chance it’ll end up being compromised or just a bit crap. The Chameleon above is a good example. Old 26″ chameleon frames in small weren’t actually a million miles away from DJ geometry but a 170mm fork and 690g retro DH rims are both awful choices to fit to any DJ bike. even more so a 20yr old Alloy XC frame.