Top down(ariel) Shooter game and question

What would be the best route at setting up scenes for a top down shooter game? Im still getting a feel for Unity and started placing randomly create items/scenary but when i go and check out to make sure they are at the same height, they are not.

I did the fps Tutorials and decided to grow with it to what i was trying to do. I am not sure what i am doing wrong with this part but for some reason the missiles I made are flying through other objects/dissapears as soon as it appears in my other project only difference is i have a model of a missile instead of a ball. I play the game, they fire but i get an error message "There is no ‘collider’ attached to the “missile(clone)” game object. I would try and add a collision mesh/cube to fix the problem but it brings the problem of the missiles quickly dissapearing. I tried pulling the “launchers” in the front of the ship thinking it was somehow colliding with the player itself but it didnt fix the problem.

Any advice is greatly appreciated

Why would you expect randomly placed objects to be at the same height as each other? How are you placing them?

Confused… how can something disappear from one project and appear in another? It doesn’t matter what your model looks like / is of, it will behave as scripted.

Totally lost… ‘they’ who fire? clone? of what? are you using Instantiate() somewhere? what problem of ‘the missiles quickly disappearing?’ launchers?.. ???

See if i can explain a little better.

When I was doing the fps tutorial, it shows step by step of how to make a rocket launcher, how to make it shoot a rocket, etc.
I took they same script and settings for the player, launcher and rocket and set up the same way in another project except i used my own models.
When i go to shoot the missiles, they work but they do not have a collision attached to them.

I tried to fix that by giving them a collion box however when i go to fire. They do seem to disapear even though the engine still recognizes they are still flying. I did check to make sure the ship or the empty had no collision meshes attached to them.
(the two specks in front of the ship suppose to be the particles of the missile but disapears with it also, only reason we see it is from the delay before the particles start emitting)

images dont show ImageShack - missile.jpg
ImageShack - missile1c.jpg