When to put him outside?
 

I have a 5 year old Spur thigh (Testudo graeca). In the summer, on warmer days we let him roam the garden (it's escape proof) but at night bring him in to his "table". On the colder days we keep him in but let him wander the house.

I plan to build an appropriate outdoor area for him so he could be outside at night too - but was wondering over what time of year is it "normal" for him to be out overnight?

Thanks

I have a Hermann. He is usually out 24/7 between late May to late September without additional heat/light except for a couple of cold frames...this could be prolonged in early Spring and late Autumn with artificial heat/light.
I generally wait until the night time temps are consistently 10 degrees F.
However, I have left him out at night in temps around 7 degrees which is fine as long as it just the odd night, not prolonged and the days are hot...Remember that if your tortoise is roaming the house over a prolonged period, he will not be getting UV.

Does he sleep in the cold frame of his own accord?

A lot depends on where you live as to when your tortoise can go outside 24/7. Generally its when the threat of frosts has gone.
I live in the SE of England, and my tortoises are outside 24/7 from around April/May depending on the weather. They have a GH which is heated in the late Autumn and early Spring. But is switched off in May. If we have a dull day then they dont come out (its their choice as they can come and go as they please) if the sun comes out so do they:0)
If you live further north then its a little later in the Spring for them to be out all the time.
:0)

Yes, most of the time. As there are no bottoms on either of my cold frames and various plants and pots inside them he usually digs down beneath the pots.
I think terracotta pots act as a kind of storage heater (holding the heat of the day) and are that little bit warmer through the night.
Occasionally he will dig in under the Carex grasses outside the cold frame.
I just let him do as he wants. He generally knows where to go and at what time.

It's also worth remembering to be aware of potential predators, especially at night. So please bear this in mind when designing the outside area.

If you put him inside a few times for a week, they soon find their own way back to the CF. As on colder days CF's hold quite a lot of heat for them:0)
My CF's are set on bricks with a gap so they can come and go as they please within their enclosure:0)

all good advice on here. I do bring some of the younger ones in under cover (manually!) if its dreadful weather such as ram rod rain, but it can heat up so quick again as well with our English climate so always access to outside and they usually decide themselves. Pickys welcome ! CB