Take a look at PBS Kids' Go's Draw that Habitat! This resource is linked to the PBS Kids Fetch series, which incidentally has an amazing free app that uses augmented reality to target counting and addition skills. Draw that Habitat! challenges kids to create a habitat for an imaginary animal for whom a few targeted characteristics are provided:
Draw that Habitat! has its own art pad (which is Flash-based, so non-iPad friendly) for kids to draw the picture and submit after you create an account. Submitting provides the extra rationale of "publishing" one's work, often powerfully motivating, but you will probably have to set realistic expectations about work being recognized by the site (I have no idea how many submissions they get).
The other aspect of Draw that Habitat that makes this a great Project-Based or Theme-Based Learning kind of site is that previous months' animals and habitats are featured on the Gallery page. This provides a great resource to set the context and provide examples for students. You can use the examples for picture description activities, read the rationales for why the examples were chosen for the animal, and even have the kids evaluate and "rate" the submitted drawings. So many language opportunities! You could also use previous animal descriptions (the "About this Animal") for additional practice in constructing habitats.
Although you cannot use the site's art pad and submit for previous months' animals, this is a good place to use traditional drawing materials or an app such as Doodle Buddy.