Kai wrote:
To design proper input and trigger stages counts to the most difficult and sophisticated challenges you can imagine!!
And by all these difficulties you probably will not have any reference scope to test what you design, am I write? This is like doing a heart operation with closed eyes...

But nevertheless, sounds exciting!!

Yes, "sounds exciting" is correct, however, be aware that (as Kai stated) there is so much more than just putting the components together to building a scope. I can guarantee you that the gap from "somewhat useable" to "good" (forget excellent) is enormous. While the build of a scope is not something I have seen much of, a capable engineer in the office next to mine spent 6 months trying to make a switching power supply as good and cheaper than the ones we buy - and failed. Design is one thing, know-how is another. Just to mention one thing: when you go for 100 MHZ there are things like transmission line effects on your PCB>

So in conclusion "sounds exciting" is right "sounds simple" is not.

Erik