Welcome,I will do my best to help you with your issueI am a retired solar contractor in NH while I can answer your other questions I have no idea what the permitting process is like in Hawaii and I don't think we have any Hawaiian experts. Let's start with the roof. You want a roof that will last as long as the panels which means 25 to 30 years. Actually the panels will still produce even after 30 years but their output will be significantly degraded. There are mounting systems for every type of roof so your husband needs to familairize himself with the mounting brackets for your type of roof. The racking systems are pretty much universal and work with all standard panels. Here in NH the preferred roof is a standing seam metal roof. There are advantages to this type of roof (it sheds snow) here in New England that don't carry over to where you live but it's still a good roof and is widely used down South in the hurricane zone because of its wind resistance. Even the best asphalt shingle roofs won't last as long as the panels but if you don't plan on being there 20 years from now it's not really an issue. I'm a bit skeptical about buying solar panels from a big box store without knowing the brand of the panel. But generally panels made in China (far and away the most panels come from China) are the least expensive and have perfectly acceptable quality. I have Chinese panels on my roof from Canadian Solar ( Canadian Solar panels are made in China). Panels made in the States or Europe tend to be better quality but the quailty difference doesn't typically justify the higher price. There is no extra step re: the Federal tax credits you just need to keep the records (invoices) than prove your costs. You can't include your husbands labor costs unless he has his own company that is a corporation. Then the corporation needs to bill you and that becomes your proof of cost. Here is a link to a list of incentives available in your State. http://www.dsireusa.org/incentives/index.cfm?re=0&ee=1&spv=0&st=0&srp=1&state=HIThe Dsireusa site is the most comprehensive and up to date source for available incentives.If any part of the array will be shaded when some of the array is in the sun you might want to consider micro inverters instead of a single inverter for your system. Here is a link to Enphase . Their site explains the advantages of microinverters. The micro inverter system is a bit more expensive (and complicated) than a single inverter system but it's worth the extra expense if your site conditions have some shading. As far as the permitting is concerned your best bet (and what we did when we installed in a new jurisduction) is to go to the local code enforcement official and ask what they want. I would hold off on doing any work until you've talked to the local code authority.