Staged Construction

Design and build the infrastructure (support, cooling, signal and power distribution) for the entire device (barrel strips and pixels, and endcap pixels), and mount detectors in stages, starting with barrel strips. The advantage is that it requires only one infrastructure design, the disadvantage is that everything has to be specified very early on.
Design and build a temporary support structure for the barrel strip layers, and build a new structure when the pixel detectors are ready, transferring the strip detectors. The disadvantage is that the design and construction effort of the support structure is nearly doubled.

Design and build a temporary support structure for the barrel strip layers, and build a new structure when the pixel detectors are ready, transferring the strip detectors. The disadvantage is that the design and construction effort of the support structure is nearly doubled.