A great way to mount solar PV arrays to metal roofing is to use standing seam roofing and "S-5!" ( www.s-5.com ) aluminum clamps that squeeze down on the vertical part of the roofing (the "standing seam"). Onto those clamps you mount the aluminum rails and then the PV panels onto the rails. This will work with any type of framed panels. Its nice because it is quick, you don't have to drill holes through your brand new metal roofing and the clamps can be positioned wherever is convenient.
But mounting the panels on the roof is typically the most straightforward part of a system installation. It's the wiring, electronics and interconnection with your house electrical system that can get very complicated and can potentially get you in trouble with your electric company and/or code enforcement officials, not to mention potentially causing a fire or a shock hazard if the wiring is not done properly.
What kind of a system are you considering? Most new solar PV systems in the PNW are direct grid-tied with no batteries. That is probably the kind of system that the folks who did a site survey of your house are suggesting. Those systems can generate power anytime the Sun is shining and 'store' the energy by spinning your meter backwards through a "net-metering" agreement with your utility. As Miranda mentioned, in many places you will need to work with a licensed and approved installer to be able to capture all the benefits, tax credits and incentives available for grid-tied PV systems. The other type of system you might be considering is an "off-grid" or "standalone" system that is not connected to the utility, to use for charging batteries that you can draw from as an independent or backup source of power. A small off-grid system may not require an electrical permit and can be installed in a DIY approach more easily. You CAN claim the 30% federal tax credit for an off-grid system on your residence.
