Control your emacs frames programatically

I use these two functions to set the frame (emacs parlance for top-level window) size and the display font:

(defun arrange-frame (w h &optional nosplit)
  "Rearrange the current frame to a custom width and height and split unless prefix."
  (let ((frame (selected-frame)))
    (when (equal 'mac (framep frame))
      (delete-other-windows)
      (set-frame-position frame 5 25)
      (set-frame-size frame w h)
      (if (not nosplit)
          (split-window-horizontally)))))

(defun my-set-mac-font (name  size)
  (interactive
   (list (completing-read "font-name: "
                          (mapcar (lambda (p) (list (car p) (car p)))
                                  (x-font-family-list)) nil t)
         (read-number "size: " 12)))
  (set-face-attribute 'default nil
                      :family name
                      :slant  'normal
                      :weight 'normal
                      :width  'normal
                      :height (* 10 size))
  (frame-parameter nil 'font))

Then I have a bunch of functions like this to set my window as needed:

(defun medium (&optional nosplit)
  "Create a large window suitable for coding on a macbook."
  (interactive "P")
  (my-set-mac-font "bitstream vera sans mono" 12)
  (arrange-frame 170 45 nosplit))

(defun presentation ()
  "Create a giant font window suitable for doing live demos."
  (interactive)
  (arrange-frame 85 25 t)
  (my-set-mac-font "bitstream vera sans mono" 24))