Insulation will do little good if it is wet. Your priority at this point should be to get the roof repaired.
Build your own cabinets??!!! Turn back NOW!! :D
Insulation is fuel you pay for only once.
The best part about making your own cabinets, they come with a lifetime warranty. :)
Making your cabinets with 3/4" prefinished is a great idea. I like poplar for paint grade, but soft maple is a better alternative. It's harder than poplar and will withstand kitchen abuse better. I wouldn't worry about wear and tear on the paint. It's easily repaired. You can always use an exterior paint if you are concerned about water damage.
The most important thing is to make everything square. If you don't, installation will become very problematic.
How about getting the unfinished cabinets at Lowes or Home Depot?
They can even order you some nice pine cabinets in a afordable pricing ! That is what I did and it turned out great ! Friends of mine hung the cabinets and I am ecstatic about them!
Go and have a good look !