There are missions where you are able to play as the vehicles/droids you build as you collect minikits. You can play these missions with any vehicle etc. you have built completely by collecting all of the minikits in its respective level. However, some will be useless, as they do not have on any blasters or canons on them. There are 6 missions in total, each taking place in its respective movie (for example, the first level takes place on Tatooine, where the Pod Race is in episode one, The Phantom Menace). The goal for these missions is to collect 1,000,000 studs, with a time constraint of five minutes. You can collect studs by shooting structures made out of bricks or enemies. When you blast one of these things, you will get a fair amount of studs, with most of them being blue, making these missions fairly quick. There are silver, gold, and purple studs as well, but they are not as abundant. This mode is very similar to Collect Studs mode in the Arcade, as the containers and structures you shoot will re-spawn and still yield power-ups and studs. However, a difference between Collect Studs and the Minikit Missions is that you get to keep all 1 million studs collected! As mentioned before, there will be a handful of enemies flying around, but they won't be too much of a hassle. They are the same for every mission, and they look like a kind of Vulture Droid, but with a bluish color. For every mission completed, you will be rewarded one gold brick, yielding 6 golf bricks in total. You can use all your extras here, except the ones that enhance your stud collecting ability.
Tips, Tricks, and Extra Information
If you want to get these missions out of the way before you go through everything in Story Mode, play the level Battle Over Coruscant, as you can get all of the minikits in Story Mode very easily. The minikits will build a droid ship that you can use effectively in these missions
The rotating torpedo targets yield purple studs, but do not focus on them. They will waste your time
Be cautious of continuous blasting, as you can blast structures from a distance, and then you may not be able to collect the studs and/or power-ups inside them before they disappear
Similar to Collect Studs mode in the Arcade, look for a power-up, and then stay in the area where it is found and take advantage of the re-spawn
In the second level, I have experienced a glitch which makes the studs giant