Whatever your preference, level of experience, price range and willingness to commit to a build, there is likely to be a gunpla kit that is right for you, but if you want to make something that’s truly unique, there are few better ways than through what is known as kitbashing.
The term kitbashing, when it comes to model building, is where you create a model using pieces from multiple different building kits. It is a very common practice in professional model building, and kitbashing was used in various highly acclaimed works such as Star Wars and 2001: A Space Odyssey.
Outside of the silver screen, kitbashing is a common and pretty popular part of the model-making hobby, and whilst it is most commonly associated with Games Workshop due to how many spare bits are left over from a typical Warhammer 40,000 kit, most model kits have kitbashing scenes.
When it comes to gunpla, however, there is a lot of scope to give it a try and a lot more opportunities to fix a mistake compared to, for example, kitbashing to create custom Tau Empire battle suits.
For a start, most High Grade gunpla models made after 2007 use very similar polycaps for the joints of the model, so a lot of pieces can simply be attached as desired.
Similarly, Bandai's more recent 30 Minute Missions series of kits [Abbreviated 30MM] have been released in purpose of customising and kitbashing. The series encourages users to customise parts thanks to the 3mm pegs and holes found on all the kits to create unique builds and enter creative competitions called Customise Missions.
However, kitbashing, by its very nature, can be expensive. You will need to buy at least two (possibly more) kits to get the parts to put together and unless you plan on painting the new model yourself and adding decals, your choice of parts is limited to the colour schemes of the kits you choose to use.
There is also the potential for gaps on parts, which will need filling in with modeling putty, as well as a potential need to glue pieces together. These are just some of the things to consider, however, if you're up for a creative challenge in plastic model making, then it can be exceptional fun and you will end up with a truly unique mech design.