var creator = new PSI_Interface.IdentData.IdentDataCreator("id", "name");
var software = creator.AddAnalysisSoftware("Software_ID", "Software_Name", "Software_Version", CV.CVID.MS_Software_Name /*if available, or CV.CVID.CVID_Unknown*/, "Software_Name_for_param");
var settings = creator.AddAnalysisSettings(software, "Settings_ID", CV.CVID.MS_ms_ms_search);
var searchDb = creator.AddSearchDatabase("Database_name", "Number_of_entries_in_database", "Database_location", CV.CVID.CVID_Unknown /*or published database if in CV*/, CV.CVID.MS_FASTA_format /*or other database format*/);
settings.AdditionalSearchParams.Items.Add(new CVParamObj(CV.CVID.MS_parent_mass_type_mono /*or other CV term*/); // Add all that are search parameters
settings.AdditionalSearchParams.Items.Add(new UserParamObj("name_of_parameter", "value_of_parameter"); // Add all other search parameters
var mod = new SearchModificationObj(); // set FixedMod, MassDelta, Residues, and add CVParamObjs to CVParams
settings.ModificationParams.Add(mod); // Repeat with a new SearchModificationObj() for each modification in the search
settings.Enzymes.Enzymes.Add(new EnzymeObj() /* populate data */): // Repeat if there are multiple enzymes, exclude if there are none
settings.ParentTolerances.AddRange(new CVParamObj[]
{
    new CVParamObj(CV.CVID.MS_search_tolerance_plus_value, "tolerance value") { UnitCvid = CV.CVID.UO_parts_per_million },
    new CVParamObj(CV.CVID.MS_search_tolerance_minus_value, "tolerance value") { UnitCvid = CV.CVID.UO_parts_per_million },
});
settings.FragmentTolerances.AddRange(new CVParamObj[]
{
    new CVParamObj(CV.CVID.MS_search_tolerance_plus_value, "tolerance value") { UnitCvid = CV.CVID.UO_parts_per_million },
    new CVParamObj(CV.CVID.MS_search_tolerance_minus_value, "tolerance value") { UnitCvid = CV.CVID.UO_parts_per_million },
});
settings.Threshold.Items.Add(new CVParamObj(CV.CVID.MS_no_threshold)); // Or choose an appropriate CV term and value, if a threshold is used

var specData = creator.AddSpectraData("path_to_spectrum_file", "Name_of_dataset", CV.CVID.MS_Thermo_nativeID_format /*or other approriate format type */, CV.CVID.MS_Thermo_RAW_format /*Whatever format the file actually is*/);

foreach (var result in searchResults)
{
    var creator.AddSpectrumIdentification(specData, "spectrum_native_id", "spectrum_elution_time", experimentalMz, charge);

    // Add all of the necessary information to the identification
    var pep = new PeptideObj(match.Sequence); /* add ModificationObj() to Modifications for each modification in the peptide
    specIdent.Peptide = pep;
    var dbSeq = new DbSequenceObj(searchDb, proteinLength, "proteinName", "proteinDescription");
    var pepEv = new PeptideEvidenceObj(dbSeq, pep, peptide_start_location, peptide_end_location, "prefix_residue", "suffix_residue", false /* use 'true' if is a decoy hit */);
    specIdent.AddPeptideEvidence(pepEv); // repeat with a new PeptideEvidenceObj() for every distinct peptide/protein/location match.

    specIdent.CVParams.Add(new CVParamObj() { Cvid = CV.CVID.MS_chemical_compound_formula, Value = match.Composition, }); // Repeat with different CV term and value for each score item
}

// Tie all of the information together
var identData = creator.GetIdentData();

// Write out to file
MzIdentMlReaderWriter.Write(new MzIdentMLType(identData), outputFilePath);