monocoque
http://www.locostusa.com/forums/viewtop ... inum+frame
Lotus chassis
http://www.locostusa.com/forums/viewtopic.php?t=868
Yes you are going to have to search for the aliuminum frame it has been discussed in some detail. If you are serious about saving weight there are a 100 suggestions to save weight. If you have to have an aluminum frame it may be better to think monocoque frame than aluiminum space frame. If you decide to go with the monocoque frame then you are entering dark waters and you need to do alot of research.
For reasons discussed previously I dont think an aluminum space frame is the choosen/correct path.....
Even lotus didnt go down that road...Think Monopin at the jawfish site.
http://jawfish.proboards43.com/index.cgi
and look at the lotost frame above....Also consider that as you are building a unique frame that you will need t do a structural analysis on the frame to ensure that you are not putting yourself, your passengers, or the public at risk.
I sound like an old cautious man....but it is probaly true.