Ideas for what to grow in a greenhouse please!

Morning All,
My dad has just bought a large greenhouse (20 X 8 I think) and has said we can have one end of it to grow whatever we like. 
My question is, what can we grow at this time of year?
Obviously, next year we can grow toms, peppers, cucumbers etc and start off seedlings but as we are new to veg growing we've no idea what to do with the space now. 
Would love to try and utilise the space all year so that we get veg through winter too, is that possible?
Dad will be growing cacti so it will be heated over winter.
Please help!
Thanks.
LL xx 

If the greenhouse was being heated, then perhaps your dad might like to also invest in additional lighting and that would open up opportunities for growing a lot of tender crops a lot earlier than most!  (Heating alone could trigger "legginess" as plants struggle to find enough daylight)  Even if it's just minimal heating, it might be enough to overwinter certain frost sensitive plants such as chillies and then the following year, they'll get off to a better and early fruit start than from growing from seed.

In the meantime I'd say go for salad stuff as well - winter hardy lettuce, radish, mustard greens and pak choi, maybe carrots in deep pots 

Many thanks.
So I can use grow bags to get lettuce over winter?
I guess I'd have to find a deepish trough to sow beetroot?

I asked Dad if he was lighting it.  He said yes and that he *may* invest in some grow lights.  If he does, is there anything else I could try?
Many thanks for helping this novice!

LL xx