Always have. Get any bleeding done with. What SIZE?

I usually do 80x80 or 80ish x 90 

What I've done in the past is measure the actual mattress including the drop on sides & bottom, the maximum I would want without touching the floor (typically about 6-8" from the floor).  That makes them a little long, but gives some room when someone is in the bed to move around while still staying covered (I am cold natured).  also I don't really like seeing the dust ruffle much.  I have also folded up the corner of the quilt so that it doesn' touch the floor on the corner and tacked it to keep it there with a couple of hand stitches.  You don't see the border that way, but keeps me from tripping/stepping on it as I go around the bed.  If you like to fold the quilt over the pillows (old school style) include that as well.

Really it all depends on what you want.  Since you are making it, you can make it custom exactly how you like it.  If you are making it for a gift, I just use the standard comforter sizes plus some extra to be generous.

I like using a king-sized quilt on my queen bed.  I don't like using a dust ruffle at all.  A king gives me just the right length of "drop" for my queen bed, as I don't like the quilt to hang too close to the floor.  (I have a timed "night light" under the bed, like for short trips to the bathroom.)  But also, the adjustable bed that I bought last year is significantly taller than a "regular" bed, and I have to use a little step-stool to get into the bed without straining.  Yikes!  (I have stayed at hotels where it was difficult to get UP into the beds!)  So, I would need to measure very carefully to allow for height, and add even more inches to a "normal" king-sized quilt, if I wanted it to fall closer to the floor.  

My bed at home is not all that tall.  I'm 5 ft and can sit down with my feet touching. I just got back from a road trip and each motel I stayed at had beds that I had to climb to get up on!.  Falling out could have caused some major damage.

I kind of wonder why they have gotten so tall.

Good question.

I joked with DH that it's a plot against the elderly who are getting shorter in their senior years.

Well, mine is tall for a couple of reasons:  (1) a taller mattress than I have ever had before; and (2) the mechanical workin's of the adjustable bed is under there, and the platform on which the mattress sits is tall.  If I had it to do over again, I might not buy an adjustable bed after all.  It's nifty and all, but not very easy to turn over when you fall asleep with the head elevated.  If I want to turn to sleep on one side or the other, or if I want to simply get out of bed, I have to reach for the remote and push "flat" so I can do either one of those things.  It's difficult to get leverage to move around or get out of the bed.  I might rather have a "regular" flat bed again, but the massage feature is really nice.  Ahhhhhhh!