I had asked a similar question earlier today; thank you all who gave me answers. Since my question was limited to the first 3 rows of the table, I got stuck while writing the code for the other rows, as the row and column style changes. As it is taking me a lot of time, I request you to help me produce the table as shown in the photo (either the left or the right, whichever possible).
The texts in the last 2 columns are sample texts; the actual text is long. So the table will be about 3 pages.
Below is a sample working code:
\begin{table}[htbp]
\centering
\caption{Add caption}
\begin{tabular}{|l|p{6.72em}|p{15.335em}|l|}
\toprule
\multicolumn{2}{|c|}{\textbf{RIBA Work Stage}} & \multicolumn{1}{c|}{\textbf{Description of Key Tasks}} & \multicolumn{1}{c|}{\textbf{Core BIM Activities}} \\
\midrule
\multicolumn{1}{|c|}{\multirow{2}[4]{*}{\begin{sideways}\textbf{Preparation}\end{sideways}}} & \multicolumn{1}{c|}{\textbf{Appraisal}} & Task desciption for Appraisal & \multicolumn{1}{l|}{\multirow{2}[4]{*}{• BIM Activity 1\newline{}• BIM Activity 2\newline{}• Data drop 1}} \\
\cmidrule{2-3} & \multicolumn{1}{c|}{\textbf{Design Brief}} & Task desciption for Design Brief & \\
\midrule
\multicolumn{1}{|c|}{\multirow{3}[6]{*}{\begin{sideways}\textbf{Design}\end{sideways}}} & \multicolumn{1}{c|}{\textbf{Concept}} & Task desciption for Concept & \multicolumn{1}{p{11.665em}|}{• BIM Activity 1\newline{}• BIM Activity 2\newline{}• Data drop 2} \\
\cmidrule{2-4} & \textbf{Design Development} & Task desciption for Design Development & \multicolumn{1}{l|}{\multirow{2}[4]{*}{• BIM Activity 1\newline{}• BIM Activity 2\newline{}• Data drop 3}} \\
\cmidrule{2-3} & \textbf{Technical Design} & Task desciption for Technical Design & \\
\midrule
\multicolumn{1}{|c|}{\multirow{3}[6]{*}{\begin{sideways}\textbf{Pre-Construction}\end{sideways}}} & \textbf{Production Information} & Task desciption for Production Information & \multicolumn{1}{l|}{\multirow{3}[6]{*}{• BIM Activity 1\newline{}• BIM Activity 2\newline{}• Data drop 4}} \\
\cmidrule{2-3} & \textbf{Tender Documentation} & Task desciption for Tender Documentation & \\
\cmidrule{2-3} & \textbf{Tender Action} & Task desciption for Tender Action & \\
\midrule
\multicolumn{1}{|c|}{\multirow{2}[4]{*}{\begin{sideways}\textbf{Construction}\end{sideways}}} & \multicolumn{1}{c|}{\textbf{Mobilisation}} & \multicolumn{1}{l|}{Task desciption for Mobilisation} & \multicolumn{1}{l|}{\multirow{2}[4]{*}{• BIM Activity 1\newline{}• BIM Activity 2\newline{}• Data drop 5}} \\
\cmidrule{2-3} & \textbf{Construction to Practical Completion} & Task desciption for Construction to Practical Completion & \\
\midrule
\begin{sideways}\textbf{Use}\end{sideways} & \textbf{Post Practical Completion} & Task desciption for Post Practical Completion & \multicolumn{1}{l|}{\multirow{2}[4]{*}{• BIM Activity 1\newline{}• BIM Activity 2\newline{}• Data drop 6}} \\
\cmidrule{1-3} \begin{sideways}\textbf{R \& D}\end{sideways} & \textbf{Model Maintenance \& Development} & Task desciption for Model Maintenance \& Development & \\
\bottomrule
\end{tabular}%
\label{tab:addlabel}%
\end{table}%
