Audi a3 1.8t front brake discs and pads help

[L3WJX]

Hi have not been on here for a long time so a big hello again,
I am looking for some brakes for the front mabie the rear as when i come to a fast stop sounds like a rollercoaster stopping,this mabie due to the speed but i dont like it,its a 1.8t 230bhp with standard brakes i would like to no if any body can point me in the right way,im not looking to spend loads and wouldnt mind second hand ones

Thank you L3WJX