hi am think of doing a girl verson of laharl from disgaea but don't now were to start and i had a idea to u a boob-tube top and keep the rest the same but longer blue hair if u have some good ideas for this or like the idea do comment

Do some research, go onto deviantart and see if people have done gender switches before or just get creative. I usually find a croquis (fashion template) and then draw away until I get a version that I like. Same goes for gijinka. It's things like this you can't really get wrong, so just take a stab at it and you could always post up designs later and ask for feedback.

ok good think thank u

One thing I think is important is to go for it a much as you would a normal cosplay. Do the wig and everything you would do for the male version of the character.
One thing I think is very important is to keep the character in mind as much as the physical appearance. Think of what the female version would actually wear and if what you have reflects the character. So if they are a shy character, don't do a design that has them walking around in an ultra sexed up version. If you keep the character in mind as much as the design, you'll come up with something interesting I'm sure.

Have fun with it, whatever you do though.