i had the same problem.i followed another answer on a post here and it worked
here s what i did:i downloaded sdk tools package https://dl.google.com/android/repository/tools_r25.2.3-windows.zip then you extract it to C:\Users\CURRENT_USER\AppData\Local\Android\sdk.
you 'll need to replace the current user.then build again.this worked for me
here’s the link to that post if you want to
https://forum.ionicframework.com/t/error-could-not-find-gradle-wrapper-within-android-sdk-might-need-to-update-yo-ur-android-sdk/22056
and check trisna1192 answer