Tbh, Green Flips are worth more than Full Sparrow but it wouldn't be a bad trade to make, especially if you plan on keeping the Sparrow (not trading for value). Something to take into account is that people who are trading Full Sparrow are making it super convenient for you, giving them some leverage on the trade. Another thing to take into account is that Sparrow's value can only drop, not rise, in the near future, giving you some leverage.
As
@Smee stated...
Vest ~ 6 Walls
Pants ~ 2 Walls
Hat and Shoes ~ 1 Wall ea
Green Flips ~ 12 Walls (I have had no luck offering 10 Walls for Green Flips, and some people even say closer to 15 although I think that is a bit much so...)
Edit: I have seen Minnie + a few Walls for Green Flips quite a few times over the past few months so that can kinda give you an idea of Green Flips worth too.
If you are willing to hold the Green Flips, I can get Full Sparrow and trade you for the Flips. I could even add a few magic pins of your choice. I already have the Vest which is by far the toughest thing to get. I would have the other pieces in no time. I also saw you mention you are most interested in the Vest so we could also work out a deal like Vest + stuff other than Sparrow for Flips. Green flips are necessary for a Slytherin lol.