\fill[lightgray,draw=black] (0,0)       rectangle (0.5,1);
\fill[lightgray,draw=black] (1.25,0.25) rectangle (2,1.5);

\draw[gray] (0.5,1.15) -- (0.5,1.35);
\draw[gray] (0.825,0.25) -- (1.025,0.25);
\draw[gray] (0.825,1) -- (1.025,1);

\draw[ {Latex[round,scale=0.7]}-{Latex[round,scale=0.7]}
  ] (0.925,0.25) -- (0.925,1) 
  node[midway,left,fill=white,font=\footnotesize,inner sep=0.7pt] {$l_{\mathrm{p}}$};

\draw[ {Latex[round,scale=0.7]}-{Latex[round,scale=0.7]}
  ] (0.5,1.25) -- (1.25,1.25) 
  node[midway,above,fill=white,font=\footnotesize,inner sep=0.7pt] {$s$};

\draw[ {Latex[round,scale=0.7]}-{Latex[round,scale=0.7]}
  ] (0,0.5) -- (0.5,0.5) 
  node[midway,above,font=\footnotesize,inner sep=0.7pt] {$w_1$};

\draw[ {Latex[round,scale=0.7]}-{Latex[round,scale=0.7]}
  ] (1.25,0.875) -- (2,0.875) 
  node[midway,above,font=\footnotesize,inner sep=0.7pt] {$w_2$};