gistfile1.m

# In my init/setup
    // Register the header
    [self.collectionView registerClass:[DummyView class]
            forSupplementaryViewOfKind:UICollectionElementKindSectionHeader
                   withReuseIdentifier:kJJUserJujuLibraryHeaderIdentifier];


# This is being called
- (CGSize)collectionView:(UICollectionView *)collectionView
                  layout:(UICollectionViewLayout *)collectionViewLayout
referenceSizeForHeaderInSection:(NSInteger)section
{
    return CGSizeMake(CGRectGetWidth([UIScreen mainScreen].bounds), 56);
}

# This method is never called
- (UICollectionReusableView *)collectionView:(UICollectionView *)collectionView
           viewForSupplementaryElementOfKind:(NSString *)kind
                                 atIndexPath:(NSIndexPath *)indexPath {
                                   assert(false);
                                 }

gistfile2.m

@interface DummyView : UICollectionReusableView
@end

@implementation DummyView
- (instancetype)initWithFrame:(CGRect)frame {
    self = [super initWithFrame:frame];
    if(self) {
      self.backgroundColor = [UIColor orangeColor];
    }
    return self;
}
@end