You can say you wanna build a redstone computer without having any prior knowledge of redstone. But I can also say I wanna have a million dollars, without having any money before that. I'd have to win the lottery, and you'd have to miraculously place each block randomly in the proper spot.
If you wanna learn how to make a redstone computer, start smaller. Make a few more basic redstone things. A 2x2 door, a 3x3 door and a 4x4 door. Start hiding redstone, and then get into more in depth redstone. All the bugs, and all that. Start learning about the parts you'll need in a redstone computer, and build them all seperately and then go ahead and put them together.
But don't start with a redstone computer, you'll never do it unless you've got a tonne of dedication to the project.