Outlook do not support to import such contact files and using of special tool which allows to import multiple contacts from a single VCF file is required. Roundcube contacts will be saved into single contacts.vcf file.
Here is how to convert emails from Roundcube to Outlook PST file:
Free limited version is available for the trial purposes. If you want to import multiple eml files to Outlook it is required to use the special tool called EML to Outlook Transfer. Microsoft Outlook allows to open a single eml file only and do not support the importing of eml files. The email importing tool described below will handle the folders conversion as well. You may create the email folders at your hard drive to save emails to the corresponding folders.
Roundcube is free open-source email software for web.