Some people have made some amazing ones. It would be beyond my skills lol. There are a few youtube videos around on making diy cages. Someone on here made a nice one using two large lack tables on top of each other - so the bottom one made legs and a base for the cage.
90cm one
LACK Coffee table - white - IKEA
118cm one (external measurements - you'd probably lose about 12cm off that for the depth of the legs so it's just over a 100cm internally)
LACK Coffee table - white - IKEA
I thought about having a go at one, but working out doors put me off. You could mesh the sides or plexi the sides or have a hinged mesh lid or fix sliding doors.