I once did a did a costume and made an umbrella as an accessory to compliment it. I thouht i'd share my process with you. Its very easy I hope you enjoy.

Step 1: Materials

Tulle/ somewhat transparent material
lace trim
ribbon
cloth (cotton, taffeta, polyester, satin, which ever you prefer

Step 2: Find Your Perfect Umbrella

After you found the one, you strip it. very carefully cut away the fabric until it is only the spine left. don't destroy the fabric you will need it in the next step. and besure to secure the knobs you will need those too - they always disappear so easily
The first time I did this I used a child size umbrella to add to the cuteness of the costume but this time I used a big one. having done both I suggest using a small umbrella. They are easier to handle.

Step 3: Make Your Covering

For this step there are two ways to do it.
They easy way
Take your material make a mountain fold and then a Valley fold.
take the cover the just removed make a Valley fold then make another. take the whole corner and line it up with the tip of your umbrella and cut the material.

The second option would be to measur the size of one panel on the cover add a quater inch for seam width and remake The cover. this method is more exact.

I did it the easy way. because my material is tulle it was better to avoid cutting it too much.

Step 4: Fitt the Cover

Before unfolding your new cover cut a the hole for the top. sure to cut as clost to the tip as possible. when unfolded the hole size will double

Take your new cover and sew it onto the umbrella spine. Try to sew it on as close to the way the original cover was.

Step 5: Add Your Embellishments

Add your lace where you like. I put a single piece around the middle where the spine meet. You can also add beads or pearls.

Step 6: Add the Ruffles

Measure the lengthof a panel and then multiple it my the number of panels on the umbrella.

multiple that number by three and cut a half inch strip of cloth equal to that number.

Take the strip and begin to ruffle.
When it gets back to the frrst length sew it down to the ribbon.

Step 7: Attach the Frills

Sew the frill unto the umbella.

Step 8: Optional Step: Adding Bow

I added this old hair ribbon I found. You can easily recreate this with ribbons.

Glue the bow on the umbrella and then stitch it down for reinforcement.

Step 9: Original Umbrella

Here is the first umbrella with the costume mentioned in the introduction.
Its entirely up to you and depends on the look you prefer when determining the size of the umbrella