Bigger grid? I know a little trick...
Build as much as you can, from the right or top of the craft. Place a single structural part in the lower left corner of the grid. Save.
Now go to the .bp you saved and edit it, right at the end the last part will be your structural part. Change its position x value to anywhere between 0.0 and -18.0, and don't forget the comma after it or else it won't load. This shifts your build right. Or else, for a tall build, change the y value to between 0.0 and -65.0 and make sure you don't put a comma behind it. Your build will move up. Do not do both values. Save.
Now load the blueprint in-game and enjoy the extra space