To start with, I gathered as many references as I could. Because this was a costume from a tv series, I wanted it to be as accurate as possible instead of a best-guess-if-this-actually-existed-irl.
I had a really tough time figuring out how I wanted to do the sleeves. I wanted them to be long and full, but not waste too much fabric (since velvet is outrageously expensive). Another thing that really got to me was how full the dress was. I probably over did it, but the dress in the show had only a few main panels, then inserts in between to make it look really full, and drape nicely over the hoop skirt.
I debated using several patterns, but I stumbled across McCalls M6376 in my stash and noticed that it would be nearly perfect for what I wanted to achieve.
The first thing I did was cut the pattern out of muslin. I modified the pattern so that my sides and backs would be 1 piece instead of 2 contrasting colors. I also drafted new sleeves based on my "hopefully this will work out on the first try" technique.
After I had the dress all (mostly) sewn together, I drew on where I wanted it to cut off, since the original pattern covered the shoulders. Once I sewed the band to the pattern, I used sharpie to mark the pattern, and note where I wanted any changes.
After a few test fits and numerous adjustments, I had my pattern perfect, and ripped the whole thing apart. I patterened it all onto craft paper, and used that when deciding how much velvet to buy. Which was too little. Like always. I accidentally threw away my receipts, but in the end I believe I purchased 18 yards of Velvet, and it was right under $250 for just the velvet, which lead me to much crying and alcohol consumption.
I used pattern weights to keep the pieces down, even though the velvet I used seemed to be very forgiving to holes. I did the same thing out of my lining fabric. I hate lining fabric.
I sewed all the pieces together of both the fabric and lining (this is the boring part). The sleeves were completed first because they were kind of complicated. There is the top sleeve, over sleeve (the part that hangs) and under sleeve. The over sleeve had to be sewn to the lining first, then sewn in-between the velvet of the top/under sleeve. The last step of the sleeves was doing the lining.
I had the most difficult time with the over sleeves. The lining fabric would move so much if it wasn't pinned every inch, so it took like 6 tries. I was so frustrated by the end that I literally just said "fuck it, good enough" and left them how they were.
Because the dress was so extremely heavy (and slippery, damn lining fabric), I had to keep it pinned to my dress form or it would simply fall down.
Once I was happy with the sleeves, I attached the lining to the dress at the top seam. I chose not to do any top-stitching because the band that would go around at the end. Because I was running low on fabric (and apparently can't measure fabric properly - the lining was much shorter than the outer fabric...) I simply hemmed the bottom of the dress by folding it over and sewing it (not sewing it to the lining and top-stitching like I should have).
The band was kind of a unique challenge for me. I have no formal education with costuming, so with no instructions written on paper I decided to do what I'm really good at. Super-gluing shit. The band is made out of 2 pieces of velvet, the top one is larger and folded behind and glued to the back of the bottom piece. After that dried, I glued the top to bottom (in-between them) so it wouldn't drape weird when on me.
The last step (I shit you not) was super-gluing the band to the dress. It worked brilliantly, the only issue is that I can't hike the dress up by violently ripping on the band, for fear of tearing my dress off in front of anyone. I put the dress on my form before I did this, just so I knew it would look right before everything got put into place.
The belt is made of chains I purchased at Michael's, the wig was purchased off of eBay and styled, and the circlet was purchased from Etsy.
Supplies & Purchases
Queen Guinevere: Fabric/Notions/Lace $338, Circlet $82, Wig $45