In your Wix project add the reference to the WixUIExtension
In your Product.wxs (Main Install file) add a line like this
<UIRef Id="UserInterface"/>
Add the UserInterface.wxs to your project solution and customize the UI of your MSI:
<TextStyle Id="WixUI_Font_Normal" FaceName="Tahoma" Size="8" />
<TextStyle Id="WixUI_Font_Bigger" FaceName="Tahoma" Size="9" Bold="yes" />
<TextStyle Id="WixUI_Font_Title" FaceName="Tahoma" Size="9" Bold="yes" />
<Property Id="DefaultUIFont" Value="WixUI_Font_Normal" />
<DialogRef Id="ProgressDlg" />
<DialogRef Id="ErrorDlg" />
<DialogRef Id="FilesInUse" />
<DialogRef Id="FatalError" />
<DialogRef Id="UserExit" />
<DialogRef Id="InstallDirDlg"/>
<DialogRef Id="FeaturesDlg" />
<Publish Dialog="WelcomeDlg" Control="Next" Event="NewDialog" Value="FeaturesDlg" Order="2"></Publish>
<Publish Dialog="FeaturesDlg" Control="Back" Event="NewDialog" Value="WelcomeDlg">1</Publish>
<Publish Dialog="InstallDirDlg" Control="Back" Event="NewDialog" Value="FeaturesDlg">1</Publish>
<Publish Dialog="InstallDirDlg" Control="ChangeFolder" Property="_BrowseProperty" Value="[WIXUI_INSTALLDIR]" Order="1">1</Publish>
<Publish Dialog="InstallDirDlg" Control="ChangeFolder" Event="SpawnDialog" Value="BrowseDlg" Order="2">1</Publish>
<Publish Dialog="InstallDirDlg" Control="Next" Event="SetTargetPath" Value="[WIXUI_INSTALLDIR]" Order="1">1</Publish>
<Publish Dialog="InstallDirDlg" Control="Next" Event="NewDialog" Value="ExitDialog" Order="2">1</Publish>
<Publish Dialog="ExitDialog" Control="Finish" Event="EndDialog" Value="Return" Order="999">1</Publish>
</UI>
<UIRef Id="WixUI_Common" />
The complete sample of this code can be found at this answer
Look at this link, explains how to create Custom Dialogs
Good luck!