Hi so I was wondering I am thinking of making a space ship for my game but I would want it be rather large around 350m long and have versus floor so my question is , based on my understanding if I want to make that to scale in blender I would need to make it in separate parts ? or should I make it smaller and then enlarge it in my game engine ?
There is no need to make it separate parts due to scale, but it is probably wise to break something like a spaceship into different parts (depending on the level of detail...more detail = more parts).
If your game engine is Unity (and most likely even if it isn't), you will want to use 1m = 1bu (blender unit) or switch to meters here:
As NoviceInDisguise mentioned in the comments, you may want to adjust the clipping distance in the 3D view if you are working with unusually large or small objects.