Well having been inspired by a few threads and the long term desire to own a castle I took the plunge and purchased the small Renedra Castle. Small is relative here since the box that arrived was massive! Not easy smuggling that one into the house.
I don't want to just build it straight since to me it looks quite boring with four towers and four walls in a rectangle and also unlike any western European medieval castle. So a plan has been hatched to hack the thing up.
First off was to build a bit of wall. That went well except I realised liquid poly cement was no good. On something with such large areas to cover it was drying at one end before finishing gluing the surfaces. So a raid of the cupboard found a tube of humbrol cement which is ideal.
Next was a gate house. I have decided not to use the upper windows except on a main keep - so the gate house is low and squat but looks OK I think.

Now the fun begins. I wanted to make an octagonal tower. This has a few pluses - it allows 45 degree bends in the walls and also looks more interesting. So I took the tower parts with the buttresses and chopped them in half. The wall was then scored and bent to 45 degrees to create a corner. I then took a floor piece and cut it in half, chamfered the edge then glued the whole lot together to create 3 sides of my octagon. That is as far as I got last night.

My aim is to build a third tower as a keep with three levels (totally straight as it comes in the box), hack a tower in half for two corner bastions and chop a couple of walls up to make 45 degree turns and finally to mash together a great hall from two walls and some window pieces. Ultimately it should let me build a keep and bailey style castle with the keep outside the bailey or a concentric style where the keep is in the bailey wall.

I should till have enough bits left over for a causeway to the keep, some additional lean to structures in the bailey and to build an entire chapel/hall made up of more of the windows. Just need to decide how to do the tiled roofing, I was thinking of using Slaters 7 mm scale embossed sheets.