I have a birthday cake to make in a couple of weeks and need to make a number 50 to go on the top . I have seen great toppers here but have no clue how to make them and stand them up on the cake . Need some help please !

You're best to start soon especially if you're making them with gumpaste so they have time to dry. I had to make two 50s for two different cakes last year (they're in my pics). I rolled out a long piece of gumpaste (I actually did a 50/50 mix with fondant as I had coloured fondant) and then shaped the numbers. I stuck the long bamboo skewers into them so they would dry in the numbers. When the numbers had firmed up a bit, I stuck them into styrofoam to dry and rounded out the part that had flattened on me. When I put them into the cakes, if there was some bamboo still showing, I put a small ball of the same colour onto the skewer to cover it up. Hope that makes sense. If you want flat numbers, I'd roll out the gumpaste relatively thick and use an exacto knife to cut out numbers (maybe print them out in a large font?) and then maybe "glue" with gum glue two 5's together with the bamboo skewer in the middle, and do the same with the 0.

We make toppers all the time from straight gumpaste. They are very popular and our customers love them! We do numbers, shoes, purses, dots, stars, etc.
Take a program like Word and print out the number the size you need it. Roll gumpaste (we use Nick Lodge's recipe) to a #1 or 2 on your pasta machine. Those are the 2 thickest settings on our machine. Lay the paper over your gumpaste. Using a very sharp xacto blade, cut through the paper and paste. Remove the paper and excess paste. We make the numbers have a long point on them so you can push the point into the cake and the number sits above the cake.
Lay the numbers to dry on a piece of 1-2 inch flat thick foam (like you would buy for a seat cushion). We live in a humid place and it takes about 2 days to dry completely. Make sure the foam is flat so the numbers don't warp.
Make sure your paste is fairly stiff or you may have some stretching and distortion. HTH!

I made a 50 for a cake I did last September (picture is in my photos, a three tier orange cake with day lilies), it was made from straight gum paste and I had made it a week in advance. However it was a warm and humid day and it fell apart. Luckily I made extra royal icing lilies and was able to top the cake in those. The birthday guy didn't know the difference. Any ideas what I did wrong??? Since then I have covered wooden numbers (from craft stores) with fondant. I am scared to try it again.

Thanks guys ,Will give it a bash over the next few days !