Yup, that's a perfect time for a shed.
I was asked about the gap in the back. We purposely leave the rafter area open for ventilation. COLD is not a problem. The shed is for a windbreak, and a dry play to lay down when it's 35-45 F rain, and when there's mud everywhere.
Also, we have another shed, about 12 x 12 in this field for the calves. But, our numbers have been increasing & the shed was getting too crowded. The calves could fit in it to lay down, but they would drag their mud covered legs against one another, and withing a day of mud season, the calves would have mud on their sides & back. Not a healthy situation. We've only just begun our mud season (about 1 week), but the calves look awesome - all fluffy & clean. Hope it stays that way.