6 feet tall by 3 feet wide is the industry standard when it comes to roll up standees. We recommend that you stick to this size since you’ll get service at different print vendors across the country. 
But, if the occasion asks for it, we also offer different sized roll up standees (as shown in the image below). The sizes are as mentioned in the list here:
5 foot (height) x 2 foot (breadth)
6 foot (height) x 4 foot (breadth)
6 foot (height) x 6 foot (breadth