Realia, much like graphic materials, have been cataloged in a variety of ways. Historically, they were cataloged into HOLLIS, but now many are added to OASIS. Currently, a curator decides whether the item will best be served in HOLLIS or OASIS.
If cataloged in HOLLIS, RDA is applied; Appendix H of Maxwell's Handbook for RDA is a useful starting point. Include 33X fields with appropriate content, media, and carrier types; 'three-dimensional form' will be the customary content type. Betz' Descriptive Terms for Graphic Materials, AAT, and TGM are useful tools when trying to assign terms.
The classification of this material depends on its ultimate location and often requires an additional note in the holdings record to designate exact location.