how about having a relatively cheap steel frame made to measure on site, make all the none viewing window sides (if you only have one) with plenty of steel re-enforcing, same on the bottom. have a bricky do the block work internally on the frame, use stainless steel ties, same as a normal wall construction. you could do a semi cavity wall, almost like a solid nine inch wall, tying the inner and outer wall together with block, the cavity will aid heat retention. then render or fibreglass the internals, glaze and weld the top bracing in. that's gotta work???