Build vs Buy for Internal Tools as a Solo Freelancer, Revisited

I built my own invoicing tool once, because the SaaS options felt overpriced for what I needed and I could build something adequate in a weekend. That weekend turned into an ongoing maintenance relationship — a bug here, a missing feature there, an hour every couple of months keeping it running — that I never tracked until I started logging my time more rigorously a year later.

Once I actually logged it, the built tool had cost me something like twenty hours over the year in maintenance and small feature additions, against a SaaS alternative that would have cost a few hundred dollars annually. At my own billable rate, I'd built myself an expensive hobby, not a cost-saving tool.

"I could build this myself" is true of almost everything a solo freelancer touches. It's rarely the right question — the right question is whether building it is the highest use of this specific hour.

Where building still makes sense

• A tool that's genuinely specific to how I work, with no reasonable off-the-shelf equivalent, where the alternative is a bad workaround, not a real product.
• Something small enough that it genuinely requires near-zero maintenance once built — a one-off script, not an ongoing system.
• A case where building it is itself valuable practice or portfolio material, separate from the tool's utility — a different calculation entirely.

The invoicing tool fit none of those criteria — invoicing is not specific to how I work, it's a solved problem with mature products, and it needed ongoing maintenance I hadn't priced in. I switched to a paid tool, and the hours I got back have been worth meaningfully more than the subscription cost every single year since.