<?xml version="1.0" encoding="UTF-8"?>
<Wix xmlns="http://schemas.microsoft.com/wix/2006/wi">
 <Fragment>
  <UI>
   <Dialog Id="CustomDlg" Width="370" Height="270" Title="[ProductName] - Setup">
    <Control Id="Next" Type="PushButton" X="236" Y="243" Width="56" Height="17" Default="yes" Text="!(loc.WixUINext)">
      <Publish Event="NewDialog" Value="WelcomeDlg">1</Publish>
    </Control>
    <Control Id="Back" Type="PushButton" X="180" Y="243" Width="56" Height="17" Text="!(loc.WixUIBack)" Disabled="yes"/>
    <Control Id="Cancel" Type="PushButton" X="304" Y="243" Width="56" Height="17" Cancel="yes" Text="!(loc.WixUICancel)">
      <Publish Event="SpawnDialog" Value="CancelDlg">1</Publish>
    </Control>
    <!-- ... More Controls ... -->
   </Dialog>

   <InstallUISequence>
     <Show Dialog="CustomDlg" After="CostFinalize">NOT Installed OR PATCH</Show>
   </InstallUISequence>
  </UI>
 </Fragment>
</Wix>