It depends on what you mean my "your own character."
1 if you want to make a character for a piece of art
2 if you want to make a character to share and sell
if you want to design a custom character, from the assets you have collected, here is what I recommend. Starting with the Actor section, you can find morphs that apply to the whole body, play around with those and mix and match them to get a rough body type. then from their it will be easier to start playing around with the shapes of specific body parts in the other tabs. the G8M for example tends to be naturally bulky so no matter what you change your character will still be bulky until you use a character morph that changes the whole body drastically.
Often you can share these body shapes with others by describing the recipe you used to creat it, list out what morphs and %'s.
now if you mean "make a character" like the characters you buy on the daz store, that is something different. Those characters are created by porting over the base G8 mesh, taking it into z brush or some other sculpting program, and sculpting by hand the new body shape, porting it back over to daz to recalculate the skeleton, and from what I have seen they also make custom skin textures.
sometimes what you can do, or what I do, is there is some detail I can't get with my assets, meaning I have to sculpt it in. so I'll port over both my character and the base G8 mesh over to blender using .obj, I'll sculpt in the detail I'll need, I'll add a shape key to make the G8 character be able to morph into the character shape I want, then I'll add another shape key where I sculpt the detail I want, I'll then turn off the shape key for my character, leaving the sculpt on the base G8 body, and I can port that into daz and save it as a morph that I can use for all my other characters. But most of the time you don't need to do that.