Answer: I sort of hate to do people's homework, especially since I may not understand the assignment that well and then you'll fail, end up living under a bridge and drinking to excess, and I'll feel guilty about it.

But it does sound fun. The assignment, that is.

Depends on how long you want the ostinato to be. Suppose we make it two measures, like the dance bass used in the Pachelbel canon. But we'll form it in such a way that the last note can be the dominant of the next pattern beginning a fifth higher.

For example, all in quarter notes ("crochets" to you)until the last note, a half (minim):

C3 G2 A3 B3 C3 E3 D3

repeat as many as desired, then next would come

G3 D3 E3 F#3 G3 B4 A4

But to keep from going endlessly higher you'd want to vary the change from one to the next ostinato. Above we went up a fifth, so on the next one we'd go down a fourth:

D3 A3 B3 C#3 D3 F#3 E3

So the first note of each one follows the circle around clockwise, and they join logically. This is admittedly no competition for Mr. Pachelbel. But maybe it's useful to consider forming whatever you do in a way that one leads to the other.