tldr - entertainment for onlookers will probably be low, but educational content COULD be high (but requires more work on your part of course)
So I think that building is way more interesting for the person who is doing the building. To keep engaged, you would have to essentially mind dump your thought processes as you go, an incessant stream of words which couldn't keep up with how fast you think/try solutions, etc.
At best, it would be a tutorial screencast on workflow, or a "how I develop" piece (which could definitely serve it's uses, possibly if you created some platform for people to share these screencasts, so people got a look at how others worked or though even), and at worst, a really boring chance for people to criticize each other.
I think the entertainment value would be very low, and learning/improvement probability is high, but it's very hard to accomplish either of those things without engagement.
Of course, You could build an entire successful youtube channel if you market yourself as "regular guy builds X" or "regular guy builds a node app" or "regular guy programs an arduino" so that people with little to no knowledge, or those who are starting out, or those who love ridiculously indepth how-to videos to watch. How you would differentiate yourself is probably how much educational stuff you could pack in there (for example: a lot of screencasts have some guy on a macbook using vim breezing through creating a node app, but what about if your audience has just graduated from a raspberry pi they got as a gift? How would they learn how to build/download/install vim? how to use vim? how to even get node installed? etc).