Hi,

Just measure the OD of the brake line with mikes or vernier calipers.
It's probably 3/16" OD.
Your big consideration should be what material do you want.
Steel and aluminum are crap, rusting out where you get salt and maybe acid rain.
I see 3/16 Nickle copper alloy tubing at Amazon and probably Ebay with a bunch of flare fittings for reasonable price. Then you'll need a flare tool, little
tubing bender, and a little plumbers tubing cutter.

Making up brake lines isn't rocket science the biggest pitfall is to remember to
slide the fitting on before doing the flare.
I see McMaster Carr has bronze tubing and that's really pricey.
Other's might comment on the ideal material for brake lines.

It's nice to have the tubing tools. A tranny coolant fitting snapped off
at my radiator in my 740. I didn't want to buy a new pre bent line from
the dealer for $45 or whatever. I had enough room to cut and splice a new section of tubing using a flare union and reused the old radiator fitting.
This was way better than having to set the car on jack stands and fool around
with the frozen fitting at the tranny under the car to replace a preformed hunk of tubing.

Have at it and you'll find it's no big deal.

Bill