how do i file the lien

Ohio Revised Code Section 1311.06 provides a sample mechanic's lien affidavit. The affidavit must be notarized and actually recorded by the county Recorder's office within the time period for filing (75 days for commercial, 60 days for residential projects). 

Interestingly enough, Ohio does not require a notice of intent to file. However, in situations where the owner of a commercial project has recorded a notice of commencement, a subcontractor such as yourself would be required to serve a notice of furnishing to the owner before working on the project, in order to secure your lien rights. You can still file a mechanic's lien, but if you didn't file a notice of furnishing, the owner may have a good defense against the lien.