I'm sorry for the extra question, but I'm not allowed to answer directly on this topic. Is there a way to not specify the size of parboxes, but just choose cell size for this?
As a MWE, you can use the one mentioned under the initial topic:
\documentclass{article}
\usepackage{array,multirow,graphicx}
\begin{document}
\begin{table}[H]
\centering
\begin{tabular}{|c|l|r|r|r|r|}
\hline
& \multicolumn{1}{c|}{Text} & \multicolumn{1}{c|}{Text} & \multicolumn{1}{c|}{Text} & \multicolumn{1}{c|}{Text} & \multicolumn{1}{c|}{text}\\
\hline
\parbox[t]{2mm}{\multirow{3}{*}{\rotatebox[origin=c]{90}{rota}}} & text &&&&\\
& text &&&&\\
& text &&&&\\
\hline
\end{tabular}
\end{table}
\end{document}
