While players cannot create their own Skylanders as of March 2015, it is a planned feature in the upcoming Skylander's game, Skylanders: Reign of Kaos. Players will be able to purchase "Create a Skylander" figures for that game and customize them in-game.
The "Create a Skylander" figures come in multiple colors and will be designated either "male" or "female". Once added to the game portal, users can select "Options" and then "Create a Skylander" to start sculpting their ideal Skylanders.
Users will be able to choose from a variety of body parts and clothing to make their custom Skylanders, as well as choosing custom move sets. Once the appearance and attacks have been chosen, each player can further customize the Skylander by recording catchphrases, choosing element types, and editing the Skylander's biography.
There have been hints from Activision that SWAP-able custom Skylanders will also be released for Skylanders: Reign of Kaos. However, there is little information currently available on the mechanics of the SWAP-able custom Skylanders.
Many fans of the Skylanders franchise have already been imagining original Skylanders. While these fan creations cannot be played in any actual Skylanders games, the creativity and thought put into these characters is noteworthy. A variety of these are displayed at the Skylanders Character Creator Wiki.