Should I build or buy my first rental

I recently purchased and rehabbed my first property (a 2/1 SF in a great area). My initial intention was to use a HELOC to add a 1/1rental by closing in the carport and screened porch. This addition is designed as a completely separate unit however it can easily flow into the existing house, creating a 3/2 with minimal work if needed. I thought this was a solid plan but have been wondering if it is better to use the Heloc to buy a separate rental property vs. building that "rental" addition.