Round only the corners that you want

gistfile1.m

UIBezierPath *maskPath;
 maskPath = [UIBezierPath bezierPathWithRoundedRect:<#view#>.bounds
                                 byRoundingCorners:(UIRectCornerTopLeft | UIRectCornerTopRight)
                                       cornerRadii:CGSizeMake(<#width#>, <#height#>)];

  CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];
  maskLayer.frame = <#view#>.bounds;
  maskLayer.path = maskPath.CGPath;
  <#view#>.layer.mask = maskLayer;