Didn't update this thread since I went on my journey. The stroller cover worked AWESOMELY!!!
I plan on adding little straps on the top of the stroller rain cover so I can roll up the sides and front when we're indoors or it's not raining anymore.
the thickness of the vinyl worked well to keep from blowing up and getting the kids wet. I made it generously so that it was not tight against them but actually kind of on a curve out - hard to explain what I did, but I cut the 2 side panels to make a semi circle once I attached the front panel to it. Clear as mud, eh?
The snaps on top did their job effectively - every once in a while a big gust would kind of go under the rain cover, but because of the snaps, I didn't have to worry about it flying away.
It really wasn't that hard to do - I already had the sun canopy on the stroller, so I just made the pattern to fit on that.
Get yourself some clothespins (to use to hold teh fabric on the stroller), a goodly piece or 2 of fabric and create your pattern pieces. I used the same pattern piece for the sides - only made sure to reverse it, lol, esp since there are wheel cutouts and the back is straight up and down, whereas the front part of the side panel is cut on an angle - shorter at top, wider at bottom to make a nice semi circle like shape on the bottom when it's all assembled.
I sewed the whole thing together using just a teflon foot and 100% polyester thread (that's what was in the machine at that moment, lol).
I also had lots of help from my 22 month old who kept on pulling the vinyl the whole time I was sewing it - also removing the clothespins I had holding the whole thing together (I didn't want pin marks in there compromising the integrity of the rain cover beyond what the sewing machine was going to do).
hth on you making your own. It really wasn't that hard to do, really. I laid the vinyl out on the floor because the pattern pieces ended up being quite large and used a pink sharpie to mark the lines for me to cut. I gave myself a generous seam allowance when actually cutting out the pieces because I knew I'd be overlapping the plastic pieces instead of actually making proper seams - does that make sense?
Now in about 4 years when I'm done with the triple stroller and hopefully the rain cover will still be in decent shape, I will sell that with the stroller on eBay as a bonus accessory.