Love this idea! I will update the script soon!
Yo, I just found this by searching UI engine in the search of the homepage. How do I use the blocks?
Welcome to Snap! Forum!
I am sorry to break it out to you, but the engine is not finished and none of the blocks actually work. Stay tuned now that we have someone to pressure us to work on the engine: you!
Another update for code that creates costumes and clones for menu items, but does not lay the clones out yet. Spot any mistakes if there is.
Also, I know that reporters as actions do not do anything yet.
I made my own engine and maybe you can be inspired by it. It’s simple in my opinion. I also have other blocks in the project from past stuff I made. Lots of good stuff. The multiple lines is a bit scuffed as it cuts off words and spaces sometimes which makes it look awkward, but I’m not concerned about that at the moment, nor interested in making that better since I want to try and make a text box for my next feature.
I made use of clones, so that it can make multiple text objects all in one sprite! I had a clone system that let me organize my clones very nicely. It could probably be optimized for easier use, but it more or less doesn’t bother me enough to do so.
Hope to see how your ui engine turns out though 
Thank you for sharing your own attempt at this (and reviving the project)! I will see what I can here use as inspiration!
As of now, I halted development of this UI engine until Snap! 12 gets released since 12 has a handy block for pen layers, [paint V] on [ V]::pen. Sans that block, I have to go through the trouble of cumbersome tweaking and debugging just for the engine to draw rectangles and other basic features then afterward safely clean up after their own mess, since anything pen resides on one universal paper.