Anakin left C-3PO without his outer coverings when they left Tatooine in Episode 1. Who finished him by the time they went back in Episode 2?
According to the novelisation for Episode II, Shmi Skywalker completed C3P0 just before her marriage;
When Anakin had left with the Jedi, 3PO had been perfectly functional, but uncovered, his wires exposed. Shmi had left him that way for a long time, fantasizing that Anakin would return to complete the job.
Just before marrying Cliegg had Shmi finished the droid herself, adding the dull metal coverings. It had been quite a touching moment for Shmi, an admission of sorts that she was where she belonged and Anakin was where he belonged.
On his own website, Anthony Daniels spoke about how the scene was originally filmed with Padme completing his coverings but that this never made it into the final cut or even onto the DVD. In the absence of the scene, the implication is left that Shmi is the one who completed him:
Q "I read about a deleted scene with a worried Threepio about its coverings and Padmé coming with a solution. I watched the DVD, and didn't see this scene in the special features. Is it really in the DVD?"
A "No. They ran out of space - odd in a space movie, so perhaps they ran out of something else. Sad too, since it was a rare moment of insight in the entire saga into Threepio's troubled personality. The missing scene went something like this... Discovered alone in the Homestead garage by an insomniac Padme - concerned by the sudden departure of her fledglingly murderous boyfriend - she asked if Threepio was happy. He soulfully confirmed that he was not unhappy, and that indeed everyone there was very kind and considerate. He only regretted that Master Annie had been made to leave so quickly - a mediclorean (sic) problem as far as I remember - and had no time to finish his handiwork as Maker and add the requisite coverings to his creation. It was very difficult to be like this. This? Enquired the feeling Padme. Naked! Replied the ashamed and sensitive droid. Naked! It simply wasn't protocol! For Threepio, existence is nothing without a proper structure of what is correct. Imagine the trauma of the intervening years as he wandered unclothed around the moisture vaporators in the liquid gaze of the nubile Beru. Protocol generally frowns on public nudity, even on the giant beach that is Tatooine.
Moved by this confession Padme's eyes dropped - metaphorically- to the empty floor where she found at her feet, a box of covering. I never noticed, said the astounded droid, whilst admitting that he was not very technically minded, in a manor of speaking - possibly an admission of total blindness would have been more accurate - Gracefully bending to rummage in this newly noticed treasure chest, the sharp-eyed ex-queen found another chest and a face and more besides - good taste requiring that some things are left to the imagination. The scene ended with a fully clothed and ecstatic droid posing for Owen and his bride under the contented eye of the resourceful Padme.
We originally shot Threepio as a puppet (see Gallery 1 for proof). However, once the scenes had been cut and processed by ILM, to the point of perfection (especially the acting), Mr Lucas realised that this was not the moment to spend so long away from Anakin making sand-people-sushi. So we had to go back and fix all the previous scenes using the fully dressed, if rusty, droid. The inference is that it was Shmi who completed her son's handiwork.
The moment never made it into the movie. And it never made it to the DVD. And I thought it was rather moving. Oh well."
In episode 1 while working for Watto Anakin is working on many different droids, not just C-3PO. We see him leave Tatooine and go train to be a Jedi, so I don't think he would have came back to finish C-3PO. So It's a pretty fair guess to say perhaps one of Anakin's friends or maybe even Watto. But in episode 5 Empire Strikes Back C-3PO is blown up and put back together by Chewy.