How to create variable height sections in FlowDocument in WPF

See more:

WPF

Hi,
I'm creating an application that requres flowDocumentScrollViewer.
Under that flowDocumentScrollViewer, FlowDocuments can be put.

I want to divide that flowdocument into 3 parts, i.e. header,body,footer
These sections should be of variable length. for that my approach was like:

Section header = new Section();
header.Background = new SolidColorBrush(Colors.Aqua);
//header.
Section body = new Section();
body.Background = new SolidColorBrush(Colors.BlueViolet);
Section footer = new Section();
footer.Background = new SolidColorBrush(Colors.Black);
myFlowDoc.Blocks.Add(header);
myFlowDoc.Blocks.Add(body);
myFlowDoc.Blocks.Add(footer);

It reflects the section in FlowDocument but I'm unable to resize these sections.
I cant even set height of these sections. Does anyone have any Idea about how to tackle this problem??