new ro medium format, which lens for mamiya rz67?

If you really really care about architecture then saving up for a small LF kit is a good idea, but you're right to get in some experience first. Don't worry about movements, just get out there and make some great photos for a year or two first, and get to know a couple of films really well. I hope you're doing your development at home - if not, you need to start!

120 rollfilm is far, far cheaper than 4x5 sheet film, especially in colour. Think $3-5/sheet (4x5) instead of 80c/frame (6x7), plus $5-$10/sheet developing costs instead of $5-10/roll (typical lab prices for colour). It doesn't matter that you can buy a basic LF setup for under $500 when you can blow $50 of film in an afternoon and have no keepers to show for it...

Polyglot is right about film costs being more for large format. You are going to burn some film at first learning a view camera. It's the only way to learn.

K.hendrik, Polyglot, Alan Gales, Ed Sawyer Thanks. My mamiya is in the post with 2 lenses. got a Polaroid back and film ready as i want to see results asap. itching to get started. but i realise it's all a learning process and mistakes are how i'm going to learn. i like people and buildings so i'm hoping between the 110mm and my 50mm i've given myself the best chance.
Need to start working a few more shifts. Might post some of my initial results.

I often shoot architectural and mostly use the 110mm, however, it is too long for indoor shots where you can't walk away from things. I bought the 65mm LA (also floating lens) and think this is one of my best lenses. I'd recommend that, but it's a havy bugger ( < 1kg) and around the same size as the 180mm. Not complaining though, it's always in my trip kit.

Cheers,
Mark