Would definitely help in mocking up plans!

When we were thinking of building about a decade ago, I bought some software and started playing around with it. It didn't take me long to realize I didn't have the knowledge to design a house properly - I couldn't figure out how to work with the terrain the house was going to be built on (steep, sloping block), I didn't know enough about the local building codes (height restrictions, bush fire protection measures) and I wasn't very good at figuring out how to take best advantage of orientation and views. My draft designs were bog standard and boring. We ended up finding a designer whose work we liked, and told him what we wanted - a 3 bedroom house, generous rooms, no wasted space, lots of storage, maximum natural lighting, energy-efficient orientation, open space living area, efficient (but not necessarily large) kitchen, decent deck. He produced a plan (and a little cardboard model) which pretty much exactly met our needs - we only had to make a few minor changes - and that was that. I think what I'm trying to say is that it's a good idea for you to know and explain what your needs and requirements are, but let the designer figure out how best to achieve them. That's what he's being paid for. By all means, give him plenty of input, but don't restrict him to tinkering with your design; let him produce his own.

Learn Sketchup is on my to do list. I use the IKEA and Reece online tools, which are good for quick mockups to help visualise the space with basic 3D rendering, but they can be a bit buggy and of course only have their own products to work with. I use Illustrator and photoshop for quick plans and mockups too, but only because I have a graphic design background.

eCadLite -- I'm assuming ours is Italian? Or somewhere in the EU. Great as you can upload heaps of catalogues to it.