It's really very simple.
You are using perf pipe and not clay pipe?
Clay pipe is laid with the loose and un-mortated. That's how the water got in to be drained off

Perf pipe needs to be wrapped with a sock of filter material to prevent it from silting up

I like to slope the run by about 2 - 5 degrees more if you can get it.

After digging the trench you need to lay a layer of gravel in. This is an important step because it's how you get the perf pipe to lay flat along it's run. If there are wavy sections or little bumps in the pipe those spots will silt up and clog the rest of the run.
Use any measuring system. Long runs you can use a surveyor's transit or a long hose with the ends fitted with Clear vinyl tubing. Put water in the hose and hold the clear parts up against a board and mark the places where the water rests. Mark posts you have hammered int to the ground so well that they won't be disturbed is you bump into 'em. They are your reference points That'll be dead level.
Male a little construction that lets you lay a string in the trench and pull it real tight.

Use your reference marks to get your slope right and grade that base layer of gravel to the string. Setting the string height so it
sits about the height of one thickness of your rake or hoe whatever tool you'll be using to drag the grade. that way you'll have a handy Visual to follow as you drag the gravel out.

Then Wrap the pipe in the sock lay it in and back fill.

I'd leave room for at least 8 inches of soil over top



Using those marks Draw your string to compose the slope by using trig to get the angle. Grade to the string

While you have the foundation exposed why not take that opportunity to water proof it. Paint it with UGL Drylok , apply a layer of poly foam sheeting.