You would need to buy a copy of the civil marriage certificate to find out the townlands (addresses) (?4 for a photocopy from GRO Roscommon), or rootsireland may have a transcript of the marriage too, though not sure whether that version will have the townlands. For Roscommon:
http://www.welfare.ie/en/Pages/Apply-for-Certificates.aspx
You have to download and print off the form. Then either post or fax it back to them. You can?t e-mail it to them. However if you want them to e-mail the cert to back to you, they will do that, so tick the relevant box.
Put the reference details on the form (anywhere). Don?t worry about leaving some boxes blank. As long as GRO have the location, name(s), year, quarter (where there is one), volume and page number they should find it.
Tradition was to marry in the bride?s church (which will be on the certificate unless it was a Registry Office marriage). That may be the place to look for her baptism and that of any siblings.