Good for you on the roof raise! In regards to the rivets, I have used both blind and solid and also welded the skin to the frame. I also made a thread which covered this matter if I recall correctly.
A few things to note.
Cleco's! Whether you go blind or solid, you will want cleco's. They are absolutely invaluable temporary fasteners. I use the crap out of them and keep on using them.
Blind pop rivets are really easy. You don't need another person, they are a little more forgiving with spatial inaccuracy and the $70 harbor freight rivet gun worked really well. I have not put my rivets through the test of time yet, but so far they have been holding up fine. I used marson 40449 clickfast pop rivets. Not because I have experience or expertise, but because aaronsb used them in his broccolli bus build
and I copy people who seem to know what they're doing.
I ended up using solid rivets at aaronsb's insistence in my earlier mentioned window skinning thread. You will need a second person to hold the bucking bar (basically an anvil) against your rivets while you beat the crap out of with a rivet gun. These arn't very hard either but these are really unforgiving in terms of size inaccuracy so be sure to measure properly, otherwise you'll have quite a few phallic looking rivets sticking out of your bus. However they feel really solid and aesthetically look nice as well. I am very glad I used these for most of my skins. They were a more work to put on then the blind rivets, but you only have to do it once. I used a boulderfly 4x rivetgun which put me back about $225.
As far as thickness goes I believe I used 3/16 diameter for both.