Paper formats are records of report.paperformat and can contain the following attributes:
1. name (mandatory) : only useful as a mnemonic/description of the report when looking for one in a list of some sort.
2. description : a small description of your format
3. format : either a predefined format (A0 to A9, B0 to B10, Legal, Letter, Tabloid,...) or custom; A4 by default.
You cannot use a non-custom format if you define the page dimensions.
For example see code below..

<record id="paperformat_frenchcheck" model="report.paperformat">
    <field name="name">French Bank Check</field>
    <field name="default" eval="True">
    <field name="format">custom</field>
    <field name="page_height">80</field>
    <field name="page_width">175</field>
    <field name="orientation">Portrait</field>
    <field name="margin_top">3</field>
    <field name="margin_bottom">3</field>
    <field name="margin_left">3</field>
    <field name="margin_right">3</field>
    <field name="header_line" eval="False">
    <field name="header_spacing">3</field>
    <field name="dpi">80</field>
</field></field></record>

Note-If it appears that your PDF report is missing the styles then report will not generate.