rockybrass.com currently has frames for about a $100 or so.
I've built several kits and my advice Is go slow and test fit often.
I've only ever used OEM complete slide assembly's and used standard lower parts kits, be aware not all 3rd party parts play nice with each other, do some research to be sure.
I also watched a"lot" of Poly 80 build videos before starting my first one.

 

If I can do this, any monkey can!!!!!

 

This is one of the better instructional videos on YouTube. The cut down snips is something I have owned for a while...not for a gun builds but have found it useful for other projects.

 

Here is really good deal!!!!!

https://www.5dtactical.com/gst-9-frame-p/gst9frame.htm

 

Very good price, but I like the Poly80 cuts better, especially the undercut of the trigger housing.

 

I think It's more popular because It has a full length slide and a concealable G19 grip length something Glock did the opposite of with the G45 I never got the point to that, I mean you know It's O.K. to put a G17 mag In your G19 If you want to right It's kinda why I carry the 17rnd as a spare.
I also have plans to build one or five of these as well.....C'mon how many walks can a guy take during self Isolation.

 

Most popular to me as I purchased for $74 around Christmas, plus I got another for my birthday. That's like a sore hoo-hoo, u can't beat it..........

 

G43 version

G26 variant

 

Went a different way with my 26 build, yes that Is a G19 on It

 

Well I have more than one truck!

 

I like the look of the gray one best