Once the old 18-story Houston Club Building here at 811 Rusk is out of the way, and someone or something agrees to set up shop inside, this is the Gensler-designed office tower Skanska has said it will begin building Downtown. Tentatively named the Capitol Tower — since the main entrance will be moved from Rusk, on the south side of the block, to Capitol — the 700,000-sq.-ft., 34-story building (and a parking garage, too) will go along with a cavernous lobby designed to connect the recently vacated tunnels to the streets above.