First of all, start with the bubble deal. We're using glass now.
Link 1: It's this but obviously modified for space.
Link 2: Here's how we build the structure. Blowing glass bubbles in space.
Link 3: It would look like some variation of this but obviously much much smaller.
As the sun
faded on its orbit and the solar panels and parabolic sun collecting mirrors became less useful, the nuclear power onboard would provide the necessary heat and artificial sunlight.
Now of course the idea would be to see how small we could make this and hopefully some applicable technology could be gleaned from the project. It would also have an interesting note in history: the first time life circled Jupiter or Saturn. Yes, it would be plants and bugs, but it would be life from Earth, and the systems we used to keep them alive might be a step towards sustainable space agriculture.
Might even send it on a course similar to a comet, maybe even flying ahead of one using it as a marker. Pick one with an orbit and orbital period that makes for a good show for future generations. In a hundred years or so people look up and say, hey, see that comet? One mile in front of it is "Life Pod One".