Your builds at the moment contain very similar blocks. If you wanted to mix things up a bit- try using different materials that still have a satisfying contrast. For example, if you wanted to keep a medieval style, log and wool together can be quite complementary. As for lack of structural ideas... When I can't think of anything to build, the best thing I find to do is to look at pictures of real buildings. Sometimes even when your walking around or in the car, see how the interesting houses have little things like odd beams and archways. The most important thing to keep in mind trying to come up with something original is to not forget details. Making any old house is one thing- but getting the inspiration to think of unique details and structure is another.
