This is only works for one section and on header

UIcollectionView dynamic sectionheaderSize

/// Header setup for content size calucation
class ProductHeader: UICollectionReusableView {

    @IBOutlet weak var imageView: UIImageView!
    @IBOutlet weak var detailsLabel: UILabel!
    
    class func createFromNib(product: Product) -> ProductHeader {
        let view = NSBundle.mainBundle().loadNibNamed("ProductHeader", owner: nil, options: [:]).last! as! ProductHeader
        view.setup(product)
        return view
    }
    
    func computeHeightWithContent(forWidth width: CGFloat) -> CGFloat {
        frame.size.width = width
        
        setNeedsLayout()
        layoutIfNeeded()
        
        return systemLayoutSizeFittingSize(UILayoutFittingCompressedSize).height
    }
    
    func setup(product: Product) {
        detailsLabel.text = product.details
    }
}

/// Collection view subclass
class ProductDetailsCtrl: UIViewController, UICollectionViewDelegateFlowLayout, UICollectionViewDataSource, UICollectionViewDelegate {
  var product: Product!
  
  /// Cache calcualated height   
  var headerHeight: CGFloat = 200.0
  
  override func viewDidLoad() {
    super.viewDidLoad()
        
    // Calculate and cache header height after all content setups.
    let headerView = ProductHeader.createFromNib(product)
    headerHeight = headerView.computeHeightWithContent(forWidth: view.bounds.width)
    
    // Register header nib
    let headerNib = UINib(nibName: "ProductHeader", bundle: nil)
    collectionView.registerNib(headerNib, forSupplementaryViewOfKind: UICollectionElementKindSectionHeader, withReuseIdentifier: ReusableView.ProductHeaderView)
  }
}

/// Adjust header height
func collectionView(collectionView: UICollectionView, layout collectionViewLayout: UICollectionViewLayout, referenceSizeForHeaderInSection section: Int) -> CGSize {
  if section == 0 {
    return CGSize(width: 0, height: headerHeight)
  } else {
    return CGSizeZero
  }
}