LEGO STAR WARS: The Force Awakens

The walkthrough writers give a good description on completing the level:

Head right down the stairs, and push the first block right and then up. Push the second block right, head across and smash the glowing objects in the foreground. Build a platform to continue right. As FN-2187, grapple and pull the block down and then push it further right. Jump the gap and do the same with the second block, this time pushing it left to make a bridge. Smash the object to the right of the sleeping droid, and rebuild and alarm clock. As the droid (R-3P0), head back over the bridge left and access the gold panel. Match the sequence shown on screen.
Red Brick Available: You can get the Red Brick in the background by multi-building forward and heading over the bridge. This Red Brick will net you Fast Interact when you're next in a hub world and have another 200,000 to spend. It's not as much of a priority as Stud Magnet.
To continue, multi-build right to create a lift. Head up and shimmy across the front of the security room, then jump to pull the lever. Smash the multi-build again and rebuild left. Press at the back of the super-grapple to pull down the entire wall. Smash the build one last time and build right again to reactivate the lift, allowing you to get into the security room. As FN-2187 complete the First Order matching puzzle at the back. Head out the back door for another Blaster Battle.

Take out everyone in the first wave, and then you'll have to deal with the turret. Peek above the left barrier, aim at the grapple point and mash . This turns off the barrier, leaving you free to destroy the turret and remaining Stormtroopers.

To take out the final giant turret you need to target the explosives to the right of it to make a further cover point to your right. Head over there as Poe and use the binocular point to scan the turret's near side. Aim for the green pulsing lights while the turret is pointed away and destroy them. Head to the left-most barrier now and repeat the process for the other half of the turret. Press near the TIE fighter to get in.

Time for a floating shooting gallery sequence. First blow up the security tower, then two sets of four stationary TIEs. Finally destroy the two ground turrets.

The final sequence is free-flying space combat. You'll need to destroy 10 of the larger turrets dotted around the top and bottom sides of the ship, as well as along the inner edge. You'll know if you'll hit one as you'll see an 1/30 appear (destroying all 30 nets a Minikit). Once 10 are destroyed, you'll need to take out the three purple points on top of the Star Destroyer using Proton Torpedoes dotted around or awarded for destroying certain TIEs. Once you've got them all, a short on-rails sequence has you shooting at incoming missiles and TIEs until your ship explodes.

After the video, you're on Jakku as Rey. Complete a sand-boarding sequence and then destroy the alien waves. Break the glowing object in the foreground in front of the big mechanical animal thing. Multi-build right to tame the beast and reveal a binocular scan point. Look at the metal wall directly ahead to find a smash point. You'll need to get on the beast thing and smash the wall with it. Activate the BB-8 switch and then head up into the spherical structure as Rey. Head around to the right across boost pads and climbing bars until you pull a lever, which activates a BB-8 switch, which opens the door.

In the next area, head left until you see some glowing breakables. Smash and rebuild the one near the back glass to reveal a hole in which you can fling your stick. Use it as a swing bar up to the left platform. Use the boost pad to jump the gap and mash to save yourself from falling. Push the box of scrap off to the left and jump down. Build the BB-8 pad and send him up. Head right until you see a small grate in the background that BB-8 can use as a shortcut back downstairs. Once through, complete the lock puzzle on the right. Rey can now jump up and head left until you see the two parallel walls at the back, which Rey can jump between to get up to the next level. Head right again, slide under the structure, boost pad right and then scale the climbing wall. Smash the objects and multi-build forward and right. Use your staff with the machine and turn anti-clockwise. BB-8 can now get up, so smash the multi-build and this time rebuild bottom-right to make a BB-8 switch. Push to the right with BB-8 to open the door.

Here is a video walkthrough:
Credit to HappyThumbsGaming.

It's an easy one to get... except when the game almost always crashes on this level for you.

I found that it crashed on me in the second and third segments. The second segment crashed a bit after both getting all the 5 Tie Bombers for a minikit and the 30 cannons on the Star Destroyer for another minikit. It crashed on the third segment on the way down to the planet. This one appeared to occur when constantly firing.

How did I get around this? I did a run through getting the two minikits specified above then saved and exited. Then did a second run through doing the minimum (including not continuosly firing) to get to the end when the achievement actually popped. I did it this way around but I reckon the order doesn't matter. You can, of course, go back for the minikits in a subsequent play through of the level.

I hope that you don't have this issue but if you do then I hope that this helps you.