Having done that, let me mention a few things.

1) drip is no good for thickly seeded vegetables, such as carrots or
garlic. Drip is good for larger plants with a spacing exceeding 12
inches. For carrots, you will have to water the usual way. This will
generate an extra variable in your crop rotation. Now garlic, carrots,
lettuce, parsnip, small greens all have to go together in one bed that
may or may not have drip and you may or may not want to make provisions
(extra valves in the lines) so that that bed does not get watered (if
you want to save water).

2) I bought online, and it was high quality piping. But then I needed
connectors and adapters which I had not ordered, so I had to find a
local supplier. They had everything the onlinestore had, cheaper and
slightly worse quality. Buy locally.

3) Think before building the drip system. I just switched from 2
lines/bed to 4 lines/bed, and pulling those pipes out of buried joints
was hell. No wonder they don't leak at the joints. You want one line
for each foot of bed width (I have 4 for five feet, as a matter of
fact).