Metropolis

I'm not certain of your approach... Ideally you should ADD a "Card Type", like "Events". These Event cards could allow you to steal a Design from your opponent tableau, allow a player to steal randomly a card from his opponent's hand, force a player to skip his turn, steal a Material card, etc.

These are "limited" ideas - since I really don't know your game. But I think if you follow the IDEA proposed and add Events to your game, you'll increase Player interaction without convoluting the End Game condition.

Just my thoughts.

Ok, so let me get this straight:
you have a bunch of cards you can't build but other people try to build them in order to eliminate you.
You spend resource type cards in order to build the cards others have.
The winner is the player with no buildings themselves but who has built everybody else's building?

What about labour, construction machinery and transport?
These would effect another thing I'm missing which I think could play a big part in your game: time.
With all the materials in place a player might find a ticking time-bomb and frantically rush to assemble someone else's buildings before the number of turns expires and the building is complete. The more points the building is worth the longer it takes, but of course there will be some exceptions and of course the right transport, labour and machinery(/tech) cards could change the time. Perhaps a player could play some of these on buildings being built to eliminate him?

I may have completely missed the point in which case ignore my suggestions.

I like the idea of turning the game into a City Building type of game... you have the board cards with great pictures of little known innovative or incredible Buildings malls, airports, concert halls, neighborhoods, parks, highways, etc... you get to build a city with those cards and with certain stats as a famous architect. Buildings are a square or rectangle, parks are octagons etc.... Values of real estate dominate the game's economy getting next to the park, beach or river increases value. Players place tokens as they each try to own all or part of each piece of real estate.... being next to the park, or being next to a run down neighborhood all affect your score. Improvement cards can help starve off when another player slaps a slum next to your high valued park, or perhaps you have enough Masonry cards to improve the slum and make a killing in real estate value... It would be great to incorporate dealing with the government, voting on certain laws....Just a thought. I love your cards you've already got together. The art is great on the new cards. Post your rules again.