REM can import buildings in XML form.

The attached files describe the format or schema needed for the XML:
    xmltest2.blg: a REM building file with sample data.
    xmltest2.xml: XML file that corresponds to xmltest2.blg.
    rem-blg.xsd: XSD schema generated from xmltest2.xml.

Notes:
- There is usually a one-to-one correspondence between the XML elements and the REM input screens. If you can enter a value into REM/Rate, it should also have a matching XML element. 
- Almost all elements in the XML file are optional (but the XSD hasn't been updated to reflect this; need to add some minOccurs attributes).
This means that you can specify partial components (e.g. a wall with only the R-value and nothing else; or a building with only the location specified).
- The XSD isn't final yet. It can lag behind the XML because it is generated from the XML.
- The XSD is not used internally by REM for validation. It is really just a reference for developers wanting to create XML import files.
- Enumerations haven't been added to the XSD.
For now, you'll have to use the REM/Rate application for reference. For any field which has an enumerated value, look for the corresponding listbox in the application. The list of possible strings are the same.
The Export Format Report (under Help menu) also has these string lists.