Time for action — making the cabin
The cabin is made with extrusions, as was the boat. By copying faces from the hull as the basis for the cabin, you will make sure that the cabin will fit snugly on the hull:
Press Z to toggle the Viewport Shading to Wireframe.
Press Shift + D to copy the cockpit floor. Press Enter. Press P to separate the duplicated faces. Choose Selection as seen in the following screenshot:
Press the Tab key to go into Object Mode. Press A to deselect all objects. Select the copy of the cockpit floor that you have just made with theRMB.
Press M, 2 and then Enter to move it to Layer 2.
Press Numpad 3 to return to the Side view.
Press 2 to go to Layer 2, or use the Layers controls in the 3D View header.
Press Numpad 7 to get the Top view.
Press the Tab key to go into Edit Mode.
Press A to deselect all faces.
Press B and use the mouse to select the faces that are in the cockpit area and not in the cabin area.
Press X to delete the selected faces. Choose Faces from the pop-up menu...