how draw 3D just using the math?

[Cambalinho]

from what i have learned from others forums and tutorials, i know convert from 3D(X, Y, Z) to 2D(X, Y):

x2D = (x * L) / (z + L)
y2D = (y * L) / (z + L)

the 'L' is the distance between the position object\dot and the player\camera.

class Console{
public:
    HWND myconsole;
    HDC mydc;
    Console()
    {
        myconsole = GetConsoleWindow();
        //Get a handle to device context
        mydc = GetDC(myconsole);
    }


    ~Console()
    {
        ReleaseDC(myconsole, mydc);
    }


    operator HDC()
    {
        return mydc;
    }


    operator HWND()
    {
        return myconsole;
    }


    RECT GetWindowSize()
    {
        RECT RectWindow;
        GetWindowRect(myconsole,&RectWindow);
        return RectWindow;
    }


    void Clear(COLORREF Color=RGB(0,0,0))
    {
        //Clear:
        RECT RectWindow;
        GetWindowRect(myconsole,&RectWindow);
        RectWindow.top=0;
        RectWindow.left=0;
        FillRect(mydc,&RectWindow,CreateSolidBrush(Color));
    }


}Console;

after knowing these i drawed a rectangle that scales when i move back and front:

//draw a rectangle        HPEN hWhitePen = (HPEN)GetStockObject(WHITE_PEN);
        HPEN hOldPen = (HPEN)SelectObject(Console, hWhitePen);
        POINT points[5] =
        {
            { (X * MeDistance) / (Z + MeDistance), (Y * MeDistance) / (Z + MeDistance) },
            { Width+X, (Y * MeDistance) / (Z + MeDistance) },
            { Width+X, Height+Y },
            { (X * MeDistance) / (Z + MeDistance), Height+Y },
            { (X * MeDistance) / (Z + MeDistance), (Y * MeDistance) / (Z + MeDistance) },
        };
        if(MeDistance-Z>=-1 && MeDistance-Z<=100)
        {
            HBRUSH hBrush1 = CreateSolidBrush(RGB(121, 90, 0));
            HBRUSH holdBrush = (HBRUSH)SelectObject(Console, hBrush1);
            Polygon(Console, points, 5);
            SelectObject(Console, hOldPen);
            SelectObject(Console, holdBrush );
            DeleteObject(hBrush1);
            DeleteObject(hWhitePen);
        }

doing the same way, i tried draw the floor without success

//Position and Size Floor:        int FloorX=0, FloorY=1000, FloorZ=0,FloorWidth=1000, FloorHeight=100, FloorZWidth=1000;


        //floor vectors:
        POINT FloorPoints[5] =
        {
            { (FloorX * MeDistance) / (FloorZ + MeDistance), (FloorY * MeDistance) / (FloorZ + MeDistance) },
            { FloorWidth+FloorX, (FloorY * MeDistance) / (FloorZ + MeDistance) },
            { FloorWidth+FloorX, FloorHeight+FloorY },
            { (FloorX * MeDistance) / (FloorZ + MeDistance), FloorHeight+FloorY },
            { (FloorX * MeDistance) / (FloorZ + MeDistance), (FloorY * MeDistance) / (FloorZ + MeDistance) },
        };


        //floor color:
        HBRUSH hBrush12 = CreateSolidBrush(RGB(0, 0, 255));
        HBRUSH holdBrush2 = (HBRUSH)SelectObject(Console, hBrush12);


        //draw the floor:
        Polygon(Console, FloorPoints, 5);
        SelectObject(Console, holdBrush2 );
        DeleteObject(hBrush12);

i need to understand what i'm doing wrong for draw the floor... can anyone explain to me?