I posted this on another about building LOS:
I would suggest using a separate build server (a basic PC with 250GB HDD/SSD should suffice) or a VPS, like a DigitalOcean droplet. Even I started learning ROM/kernel building very recently and I chose the latter. Digitalocean gives out $100 credit, when you signup, for testing purposes, which should last for a month or two. Just setup a VPS instance with 4 vCPUs/16GB RAM and add a 250GB storage block.
In addition to having sufficient storage space for the repo, the repo sync command takes roughly 20-25 minutes to complete, which is nice.
I don't want to sound like I'm promoting Digitalocean, but I hope you find it useful.