Looking for simplest way to install metal panels on existing pergola attached to house

Hello. I recently bought a house that has an existing pergola style structure attached to the house over the back patio area. It is roughly 12' (ledger to end) x ~ 18' (width) with a 3/12 slope. The pergola was installed within the last two years and other than lacking brackets and great shape. The existing "roof" however is a different story. The previous owners used plastic faux spanish barrel tile panels over "purlins" fashioned out of 4" strips of wainscot panels. There is no underlayment of any kind. They did not use any closure strips, butyl tape, or sealant of any type and absolutely did not use enough fasteners. The panels come in 8' lengths so they nested them but in such a way that water travels backward under the "roof". I'm fairly convinced that the previous owners did not care that the roof leaked for various reasons. I love my yard and patio and plan to spend a lot of time out there. Replacing the roof seemed like it should be a pretty darn straight forward project. I'm an environmental engineer (MS) - not a structural or mechanical engineer but still! I should be able to plan this out ;) But I have run into a conundrum when I went to select materials and planning out the installation. Before I say what that is I want to state: I want to do this work myself (first time doing this); I do not want to use any underlayment if at all possible; rain cover is the priority; and my project scope is adding brackets, replacing purlins and roof only. The main issue that I need help working through or around is that the (2" x 8") rafters were installed at an average of 25.125" apart o.c. with a minimum at 24.75" and a maximum of 25.5". At least those distances are consistent at the leading and ending edges but I am looking for guidance on what panel types could work for this application; what panel type and placement will work best for this application; the special considerations and tips to keep this effort basic but sound. As far as I can really tell I have two main options for type (5V Crimp and Classic Rib). I can get either in the total 12" length but like the idea of two shorter lengths to make it easier for me to handle them. Thank you in advance for assistance. J