If you want to build a bigger butt yourself, there is a glute focused workout recommended by some anon:

>Day A
Low-bar Squats
Hip-Thrusts
Abductions (and adductions if you want some inner thigh)
>Day B
RDL
Seated Good-Mornings
Abductions (and adductions if you want some inner thigh)
(sets and reps dependent on need)
>I'd recommend adding some hip-thrusts to your routine, you can do them one-legged for difficulty. I'd also consider some seated good-mornings (you could hold the weight like an RDL) where you focus on the stretched position by staying between 0 (horizontal) and 45 degrees or doing what people call one-half reps where you go all the way down, halfway up, back down, all the way up. If not seated good-mornings a pump squat would also work for this
>And you could do standing good-mornings if you wanted hamstrings, but seated ones are a unique way of isolating the glutes in the stretched positions which will grow them different to any other workout.