\documentclass[tikz,margin=3.14mm]{standalone}
\usetikzlibrary{3d,calc} % 3d is not really needed here but convenient for extensions
\begin{document}
\begin{tikzpicture}[y={(0.5cm,0.5cm)},x={(1cm,0cm)},
z={(0cm,1cm)},font=\sffamily]
\pgfmathsetmacro{\CornerScale}{1.5}
\draw (0,0,0) coordinate[label=below:A] (A) -- ++ (8,0,0)
coordinate[label=below:B] (B) -- ++ (0,5,0)
coordinate[label=below right:C] (C) -- ++ (0,0,2)
coordinate[label=right:F] (F) -- (B)
(F) -- ++(-8,0,0) coordinate[label=left:E] (E) -- (A) (E) -- (B);
\draw[dashed] (A) -- ++(0,5,0) coordinate[label=left:D] (D) -- (E)
(D) -- (C) (D) -- (B);
\draw[red] (A) ++ ($\CornerScale*(1,0,0)$) --++ ($\CornerScale*(0,0.75,0.3)$)
-- ++($\CornerScale*(-1,0,0)$)
(C) ++ ($\CornerScale*(0,-0.75,0)$) --++ ($\CornerScale*(0,0,0.6)$) --
++ ($\CornerScale*(0,0.75,0)$)
(F) ++ ($\CornerScale*(0,-0.75,-0.3)$) --++ ($\CornerScale*(-1,0,0)$) --
++($\CornerScale*(0,0.75,0.3)$);
\end{tikzpicture}
\end{document}