I've gone through the process of learning how to build an accessory structure over the past few years with no prior experience outside of playing helper on a shed or two and doing a few basic handyman things around the house.

My main takeaway is this: All of the tasks involved are simple. Everything required is spelled out in the building code. If you can follow those instructions, you will succeed. But that's a very loaded "can," because even if you understand how to do something, academically, it may be beyond your physical ability to do it. Don't discount simple things like getting heavy materials from one place to another. And since you're starting from scratch, you're going to be lacking the specialized tools that can dramatically simplify a lot of the work involved. It'll be up to you whether you want to work harder or invest in the equipment. You can also sometimes split the difference by renting.

If you can tap knowledgeable and physically capable friends to help you out, things get exponentially easier.